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Rich Web Based Applications

Introduction to Rich web Based Applications

 There is a wide range of web-based applications, which use a rich communication model such as Rich Internet Applications, mobile apps, cloud-based systems, Internet of Things based systems, etc.

Rich web - based applications

Use advanced GUIs

Use delta communication

Provide rich user experience

Delta communication,

Happens behind the GUI and it eliminates page refreshes.

Can process asynchronously and it eliminates page freezing.

Works faster and it eliminates the work wait pattern.

Delta Communication Technologies

 Delta-Communication can be seen as the power of Rich Internet Applications, and there are different Techniques and Technologies available for the development of Delta-Communication, which should be selected carefully into the Rich Internet Application development.

Simple-Pull-Delta-Communication (SPDC) can be seen as the simplest form of DC

o   Used in AJAX

o   Single XHR request to the server

o   Client-side: Native JS support

o   Server-side: special technology is not needed

Polling

Polling is used to simulate the data push.

Client side – Native JS support

Server side – Special technology is not needed

Comet

Comet is used to simulate the data push.

Long – lived XHR requests

Client side – Native JS support

Server side – Need a streaming server

Blank responses are limited

Reduce network traffic than polling

 Server Sent Events (SSE)

Server Sent Events is used (only) for true data-push

Client side - HTML5 provides native JS support

Server side – Need a streaming server

Reduce network traffic than polling/comet

Blank responses and requests are totally eliminated

 Web Socket (WS)

Web socket is bi-directional

Client side - HTML5 provides native JS support

Server side – Need a WS server

Reduce network traffic than polling/comet/SSE

Architecture

The client-side controller contains the event handlers for the GUI.

The events are triggered at the GUIs of the Views

Views are in the client-side, thus the events are triggered at the client-side

Therefore, placing the controller in the client side can be seen as an optimal solution

Client-side controller and model reduce the roundtrips to the server.

Thus, improve the performance and increase the scalability.

SPDC/AJAX

 JQuery API

1.     jQuery.ajax() - Perform an asynchronous HTTP (Ajax) request.

2.      jQuery.get() - Load data from the server using a HTTP GET request.

3.      jQuery.getJSON() - Load JSON-encoded data from the server using a GET HTTP request.

4.     jQuery.getScript() - Load a JavaScript file from the server using a GET HTTP request, then execute it.

5.      jQuery.post() - Load data from the server using a HTTP POST request.

6.      .serialize() - Encode a set of form elements as a string for submission.

7.     .load() - Load data from the server and place the returned HTML into the matched elements.

References

 https://www.researchgate.net/publication/326395849_Rich_Web-based_Applications_An_Umbrella_Term_with_a_Definition_and_Taxonomies_for_Development_Techniques_and_Technologies

http://ir.kdu.ac.lk/handle/345/1704

http://api.jquery.com/category/ajax/

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Client - Side Development – Jquery

Introduction to Jquery

 Jquery is a framework/library which can hide the complexity of pure JS.

-        Cross – browser compatible

-        Backward compatible

Jquery offers many advanced features

Change content

Change CSS

Reveal GUI element

Delta communication

 o   find – elements in an HTML document

o   change – HTML content

o   listen – to what a user does and react accordingly

o   animate – content on the page

o   talk – over the network to fetch new content

 How to use JQuery?

 1.     Using the downloaded source

                           I.          Download

                         II.          Link - <script src>”jQuery.min.js”</script>

                        III.          Use it in your code <script src>myCode.js</script>

2.     Using CDN

                           I.          Link - <script src>”CDNPath”</script>

                         II.          Use it in your code <script src>myCode.js</script>

Ways to use JQuery

 jQuery(<selector>); -> jQuery(document);

$(<selector>); -> $(document);

document provides access to the current page

 JS may execute before the page loads

              - We have to make sure the page is completely loaded, before using JS/jQuery

 JQuery Selectors

 JQuery can use CSS selectors

Additionally, provides advanced selectors to access elements faster and efficiently

 Basic Selectors

Advanced Selectors

 Descendent selector

Child selector

Pseudo classes

 DOM, DOM Navigation and DOM Objects

 DOM

  The Document Object Model(DOM) is a cross-platform and language-independent application programming interface that treats an XML document as a tree structure wherein each node is an object representing a part of the document.

The DOM represents a document with a logical tree. Each branch of the tree ends in a node, and each node contains objects.

DOM methods allow programmatic access to the tree; with them one can change the structure, style or content of a document. Nodes can have event handlers attached to them. Once an event is triggered, the event handlers get executed

o   Jquery provides API to traverse through the DOM

o   These DOM navigating APIs are faster

o   Can navigate through the DOM, element by element

$(“li”).first();

$(“li”).first().next();

 o   Can use DOM element objects

var price = $(‘<p>From $399.99</p>’);

Event Handling

 Event handlers can be set on elements, to be triggered by different events.

.on(<event>, <event handler>)

Advanced features

 “(this)” object refers to the current object within the scope

Inside event handlers, “(this)” refers to the element, the event has triggered on

 o   Data Attributes

           $('.vacation’).first().data(‘price’);

 o   Refactoring with DOM objects

          var vacation = $(this).closest(‘.vacation’);

          var amount = vacation.data(‘price’);

          vacation.append(price);

 o   Target on specific element with generic names

          $(‘.vacation’).on(‘click’, ‘button’, function() {});

 o   Filters

          Filter(‘.onsale’)

 o   CSS manipulation

         $(‘.vacation’).filter(‘.onsale’).addClass(‘highlighted’);

 o   Animation

        .slideDown()

       .slideUp()

       .slideToggle()

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Introduction to Client-Side Development

Introduction to client-side elements

Distributed systems use client-side elements, so that users can interact with.

The client-side elements include,

Views – what user see

Controller – contain event handlers for the views

Client-model – business logic and data

View Development

Browser-based clients’ Views comprises two main elements

Content – HTML

Formatting – CSS

HTML

HTML Elements

o   Structural elements – header, footer, nav, aside

o   Text elements – headings, paragraphs, line breaks

o   Images

o   Hyperlinks

o   Data representational elements – Lists, Tables

o   Form elements – Input, Radio buttons, Check boxes, Buttons

 CSS (Cascading Style Sheets)

 Used to decorate or format content.

Advantages:

Reduce HTML formatting tags

Easy modification

Faster loading

Save lot of work and time

Three main selectors of CSS

Element Selector

             -  Selects elements based on the name

ID Selector

             -  Uses the id attribute of HTML element to select a specific element

Class Selector

             - Selects elements with a specific class attribute

Advanced selectors

Pseudo Classes                                        Pseudo Elements

:link                                                         first-letter

:visited                                                    first-line

:hover                                                     first-child

Specificity:

Specificity is, which browser decide which css property values are the most relevant to an element and, therefore, will be applied.

Specificity is a weight that is applied to a given css declaration determined by the number of each selector type in the matching selector.

The following list of selector types increases by specificity

1.     Type selector and pseudo elements

2.     Class selectors, attribute selectors and pseudo classes

3.     ID selectors

 CSS Advanced features

Web fonts - Allow you to use custom fonts other than device fonts

Colors, gradients, backgrounds

Transformations and animations

Media

Media queries

Media queries can be used to check many things.

-        Width and height of the viewport

-        Width and height of the device

-        Orientation

-        Resolution

Can be used as

o   Inline CSS

o   Internal CSS sheets

o   External CSS sheets

 Inline CSS

Advantages:

Inline CSS can be used for many purposes, some of which include:

Testing:      Many     web designers use Inline CSS when they begin working on new projects, this     is because its easier to scroll up in the source, rather than change the     source file. Some also using it to debug their pages, if they     encounter a problem which is not so easily fixed. This can be done in     combination with the Important rule of CSS.

Quick-fixes:     There are     times where you would just apply a direct fix in your HTML source, using     the style attribute, but you would usually move the fix to the relevant     files when you are either able, or got the time.

Smaller     Websites: The     website such as Blogs where there are only limited number of pages, using     of Inline CSS helps users and service provider.

Lower the     HTTP Requests:     The major benefit of using Inline CSS is lower HTTP Requests which     means the website loads faster than External CSS.

Disadvantages

Inline CSS some of the disadvantages of which includes:

Overriding: Because     they are the most specific in the cascade, they can over-ride things you     didn’t intend them to.

Every     Element:     Inline styles must be applied to every element you want them on. So if you     want all your paragraphs to have the font family “Arial” you have to add     an inline style to each <p> tag in your document. This adds     both maintenance work for the designer and download time for the reader.

Pseudo-elements: It’s     impossible to style pseudo-elements and classes with inline styles. For     example, with external and internal style sheets, you can style the     visited, hover, active, and link color of an anchor tag. But with an     inline style all you can style is the link itself, because that’s what the     style attribute is attached to.

Internal CSS

Advantages

Since the Internal CSS have more preference over Inline CSS. There are numerous advantages of which some of important are an under:

Cache     Problem:     Internal styles will be read by all browsers unless they are hacked to     hide from certain ones. This removes the ability to use media=all or     @import to hide styles from old, crotchety browsers like IE4 and NN4.

Pseudo-elements: It’s     impossible to style pseudo-elements and classes with inline styles. With     Internal style sheets, you can style the visited, hover, active, and link     color of an anchor tag.

One style of     same element: Internal     styles need not be applied to every element. So if you want all your     paragraphs to have the font family “Arial” you have to add an Inline style     <p> tag in Internal Style document.

No     additional downloads: No     additional downloads necessary to receive style information or we have less     HTTP Request

Disadvantages

Multiple     Documents:     This method can’t be used, if you want to use it on multiple web pages.

Slow Page     Loading:     As there are less HTTP Request but by using the Internal CSS the page load     slow as compared to Inline and External CSS.

Large File     Size: While     using the Internal CSS the page size increases but it helps only to     Designers while working offline but when the website goes online it     consumers much time as compared to offline.

External CSS

Advantages

There are many advantages for using external CSS and some of are:

 Full      Control of page structure:      CSS allows      you to display your web page according to W3C HTML standards without      making any compromise with the actual look of the page.

 Reduced file-size: By      including the styling of the text in a separate file, you can      dramatically decrease the file-size of your pages. Also, the      content-to-code ratio is far greater than with simple HTML pages, thus      making the page structure easier to read for both the programmer and the      spiders.

 Less load time: Today,      when Google has included the Loading time in his algorithm, its become      more important to look into the page loading time and another benefit of      having low file-size pages translates into reduced bandwidth costs.

 Higher page ranking: In      the SEO, it is very important to use external CSS. In SEO, the content is      the King and not the amount of code on a page. Search engines spider will      be able to index your pages much faster, as the important information can      be placed higher in the HTML document. Also, the amount of relevant      content will be greater than the amount of code on a page. The search      engine will not have to look too far in your code to find the real content.      You will be actually serving it to the spiders “on a platter”.

 There are many frameworks/libraries/plugins to support view development

o   They dynamically generate HTML+CSS code

o   In server and/or client side

o   May have JS-based advanced interactive features

 Other tools

jQuery - A JS library, but can be seen a framework too

jQuery UI - Focus on GUI development

Bootstrap - To rapidly design and develop responsive web pages and templates

Angular - A JS framework/platform to build frontend applications

React – A JavaScript library for building user interfaces

Templates are used to maintain consistency across pages in the web site/application.

Template engines are available for both server and client sides

Client-side (JS-based) template engines - NUNJUCKS, PUG, MUSTACHE.JS, HANDLEBARS

Server-side template engines - Twig, jTwig, Thymeleaf, Apache Velocity

Plug-ins

Plug-ins are mainly to add widgets to the Views

 Component Development

 Browser-based clients’ components comprises two main aspects

Controllers

Client-model

The components of browser-based clients are developed using JS/JS-based frameworks, libraries, and plugins.

Main features of client-side development tools

o   DOM processing (dynamic content generation, change, removal)

o   Data processing

o   Data persistence

o   Session management

o   Communication

JS6 (JavaScript6)

Also called ECMAScript6

New features

JavaScript let

               - The let statement allows you to declare a variable with block scope.

JavaScript const

               - The const statement allows you to declare a constant

Exponentiation (**)

               - The exponentiation operator (**) raises the first operand to the power of the second operand.

Default parameter values

               - Default parameter values allows function parameters to have default values.

Array.find()

              - The find() method returns the value of the first array element that passes a test function.

              - function takes 3 arguments:

The item value

The item index

The array itself

Array.findIndex()

              - The findIndex() method returns the index of the first array element that passes a test function.

              - function takes 3 arguments:

The item value

The item index

The array itself

Web workers

This API is meant to be invoked by web application to spawn background workers to execute scripts which run in parallel to UI page

Web storage / Session storage

This is for persistent data storage of key-value pair data in Web clients.

GeoLocation

Identify the device location

File API

Handle the local files

Image capturing

Use local hardware

Top JS frameworks/ libraries

jQuery - Basic and simple. Cover the complexity of JS and provides cross-browser compatibility.

React - powers Facebook, Ease of Learning, DOM Binding, Reusable Components, Backward Compatibility

Angular - Support for Progressive Web Applications, Build Optimizer, Universal State Transfer API and DOM, Data Binding and MVVM

Vue – light weight, with a much-needed speed and accuracy

Generic client-side features

 Form/ data validation

Dynamic content generating/updating

Some business logic

Delta communication

References

https://www.w3schools.com/css/css_syntax.asp

https://developer.mozilla.org/en-US/docs/Web/CSS/Specificity

https://www.w3schools.com/cssref/css3_pr_mediaquery.asp

https://vineetgupta22.wordpress.com/2011/07/09/inline-vs-internal-vs-external-css/

https://www.w3schools.com/js/js_es6.asp

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Data Persistence

Introduction to Data Persistence

Information systems process data and convert them into information.

The data should persist for later use;

To maintain the status

For logging purposes

To further process and derive knowledge

Data can be stored, read, updated/modified, and deleted.

At run time of software systems, data is stored in main memory, which is volatile. 

Data should be stored in non-volatile storage for persistence.

Two main ways of storing data

       -  Files

       -  Databases

Data, Files, Databases and DBMSs

Data : Data are raw facts and can be processed and convert into meaningful information.

Data Arrangements 

Un Structured : Often include text and multimedia content. 

Ex: email messages, word processing documents, videos, photos, audio files, presentations, web pages and many other kinds of business documents.

Semi Structured : Information that does not reside in a relational database but that does have some organizational properties that make it easier to analyze.

Ex: CSV but XML and JSON, NoSQL databases

Structured : This concerns all data which can be stored in database SQL in table with rows and columns

Databases : Databases are created and managed in database servers

SQL is used to process databases

      - DDL - CRUD Databases

      - DML - CRUD data in databases

Database Types 

Hierarchical Databases 

In a hierarchical database management systems (hierarchical DBMSs) model, data is stored in a parent-children relationship nodes. In a hierarchical database model, data is organized into a tree like structure.

The data is stored in form of collection of fields where each field contains only one value. The records are linked to each other via links into a parent-children relationship. In a hierarchical database model, each child record has only one parent. A parent can have multiple children

Ex: The IBM Information Management System (IMS) and Windows Registry

Advantages : Hierarchical database can be accessed and updated rapidly

Disadvantages : This type of database structure is that each child in the tree may have only one parent, and relationships or linkages between children are not permitted 

Network Databases

Network database management systems (Network DBMSs) use a network structure to create relationship between entities. Network databases are mainly used on a large digital computers.

A network database looks more like a cobweb or interconnected network of records.

Ex: Integrated Data Store (IDS), IDMS (Integrated Database Management System), Raima Database Manager, TurboIMAGE, and Univac DMS-1100

Relational Databases

In relational database management systems (RDBMS), the relationship between data is relational and data is stored in tabular form of columns and rows. Each column if a table represents an attribute and each row in a table represents a record. Each field in a table represents a data value.

Structured Query Language (SQL) is a the language used to query a RDBMS including inserting, updating, deleting, and searching records. 

Ex: Oracle, SQL Server, MySQL, SQLite, and IBM DB2

Object Oriented model

Object DBMS's increase the semantics of the C++ and Java. It provides full-featured database programming capability, while containing native language compatibility.

It adds the database functionality to object programming languages.

Ex: Gemstone, ObjectStore, GBase, VBase, InterSystems Cache, Versant Object Database, ODABA, ZODB, Poet. JADE

Graph Databases

Graph Databases are NoSQL databases and use a graph structure for sematic queries. The data is stored in form of nodes, edges, and properties.

Ex: The Neo4j, Azure Cosmos DB, SAP HANA, Sparksee, Oracle Spatial and Graph, OrientDB, ArrangoDB, and MarkLogic

ER Model Databases 

An ER model is typically implemented as a database.

In a simple relational database implementation, each row of a table represents one instance of an entity type, and each field in a table represents an attribute type.

Document Databases 

Document databases (Document DB) are also NoSQL database that store data in form of documents.

Each document represents the data, its relationship between other data elements, and attributes of data. Document database store data in a key value form.

Ex: Hadoop/Hbase, Cassandra, Hypertable, MapR, Hortonworks, Cloudera, Amazon SimpleDB, Apache Flink, IBM Informix, Elastic, MongoDB, and Azure DocumentDB

DBMSs : DBMSs are used to connect to the DB servers and manage the DBs and data in them

Data Arrangements

Data warehouse

Big data

                - Volume

                - Variety

                - Velocity

Applications to Files/DB

Files and DBs are external components

Software can connect to the files/DBs to perform CRUD operations on data

                -  File – File path, URL

                -  Databases – Connection string 

To process data in DB

                 - SQL statements

                 - Prepared statements

                 - Callable statements

Useful Objects

o   Connection

o   Statement

o   Reader

o   Result set

SQL Statements - Execute standard SQL statements from the application

Prepared Statements - The query only needs to be parsed once, but can be executed multiple times with the same or different parameters.

Callable Statements - Execute stored procedures

ORM 

Stands for Object Relational Mapping

Different structures for holding data at runtime;

       - Application holds data in objects

       -  Database uses tables  

Mismatches between relational and object models

o   Granularity – Object model has more granularity than relational model.

o   Subtypes – Subtypes are not supported by all types of relational databases.

o   Identity – Relational model does not expose identity while writing equality.

o   Associations – Relational models cannot determine multiple relationships while looking into an object domain model.

o   Data navigations – Data navigation between objects in an object network is different in both models.

ORM implementations in JAVA

JavaBeans

JPA (JAVA Persistence API)

Beans use POJO

POJO stands for Plain Old Java Object.

It is an ordinary Java object, not bound by any special restriction

POJOs are used for increasing the readability and re-usability of a program

POJOs have gained most acceptance because they are easy to write and understand

A POJO should not;·      

Extend pre-specified classes

Implement pre-specified interfaces

Contain pre-specified annotations

Beans

Beans are special type of POJOs

All JavaBeans are POJOs but not all POJOs are JavaBeans    

Serializable

Fields should be private

Fields should have getters or setters or both

A no-arg constructor should be there in a bean

Fields are accessed only by constructor or getters setters

POJO/Bean to DB

Java Persistence API

The above architecture explains how object data is stored into relational database in three phases.

Phase 1

The first phase, named as the Object data phase contains POJO classes, service interfaces and classes. It is the main business component layer, which has business logic operations and attributes.

Phase 2

The second phase named as mapping or persistence phase which contains JPA provider, mapping file (ORM.xml), JPA Loader, and Object Grid

Phase 3

The third phase is the Relational data phase. It contains the relational data which is logically connected to the business component.

JPA Implementations

Hybernate

EclipseLink

JDO

ObjectDB

Caster

Spring DAO

NoSQL and HADOOP

Relational DBs are good for structured data and for semi-structured and un-structured data, some other types of DBs can be used.

-        Key value stores

-        Document databases

-        Wide column stores

-        Graph stores

Benefits of NoSQL

Compared to relational databases, NoSQL databases are more scalable and provide superior performance

Their data model addresses several issues that the relational model is not designed to address

NoSQL DB Servers

o   MongoDB

o   Cassandra

o   Redis

o   Hbase

o   Amazon DynamoDB

HADOOP

It is a framework that allows for the distributed processing of large data sets across clusters of computers using simple programming models

It is designed to scale up from single servers to thousands of machines, each offering local computation and storage

HADOOP Core Concepts

HADOOP Distributed File System

               -  A distributed file system that provides high-throughput access to application data

HADOOP YARN

               -   A framework for job scheduling and cluster resource management

HADOOP Map Reduce

               -   A YARN-based system for parallel processing of large data sets

Information Retrieval

Data in the storages should be fetched, converted into information, and produced for proper use

Information is retrieved via search queries

1.     Keyword Search

2.     Full-text search

The output can be

1.     Text

2.     Multimedia

The information retrieval process should be;

Fast/performance

Scalable

Efficient

Reliable/Correct

Major implementations

Elasticsearch

Solr

Mainly used in search engines and recommendation systems

Additionally may use

Natural Language Processing

AI/Machine Learning

Ranking

References

https://www.tutorialspoint.com/jpa/jpa_orm_components.htm

https://www.c-sharpcorner.com/UploadFile/65fc13/types-of-database-management-systems/ 

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Server side development 2 – REST

Introduction to REST

REST stands for Representational State Transfer.

REST is an architectural style for the service of web.

REST is

Resource based

Focus on representations

Derived using six constraints

Resource based 

Things vs. Actions

Nouns vs. Verbs

Identified by URIs 

Multiple URIs may refer to same resource

Separate from their representations

Representation

How resources get manipulated and presented

Part of the resource state is transferred between client and server.

Constraints 

1)     Client-Server

The REST is explicitly for networked distributed systems, which are based on the client-server style.

2)     Layered systems

A client doesn’t need to know whether it is connected directly to the end server, or to an intermediary along the way.

3)     Stateless

One client can send multiple requests to the server

Each request is independent

The server must not hold any information about the client state

4)     Cacheable

As many clients access the same server, often they may request the same resources

It is necessary that these responses might be cached, avoiding unnecessary processing, which may affect performance

5)     Code-on-demand (optional)

This allows the customer to run some code on demand, that is, extend part of server logic to the client, either through an applet or scripts

6)     Uniform Interface

Defines the interface between clients and servers

REST is defined by four interface constraints:

Identification of resources

Based on web’s request response model

Request = URL + HTTP Verb (GET, POST, PUT, DELETE)

Response = HTML, XML, JSON

Manipulation of resources through representations

Self- descriptive messages

Hypermedia as the engine of application state

Elements of REST style

Components

Software that interacts with one another

Communicate by transferring representations of resources through a standard interface

Connectors

Represent activities involved in accessing resources and transferring representations

Connectors are abstract interfaces for component communication

Key aspect of REST is the state of the data elements, its components communicate by transferring representations of the current or desired state of data elements

REST manages data in following ways.

Render the data where it is located and send a fixed format image to the recipient.

Encapsulate the data with a rendering engine and send both to the recipient.

Send raw data to the recipient along with the meta data.

RESTful URLs

 URL is the key technique in RESTful communication

The API of the RESTful service is a set of URLs

Operation = Read, Verb = GET

Collection

SLIIT.com/students/

Single item

SLIIT.com/students/IT123456

Multiple items

SLIIT.com/students/IT123456;IT456456;IT998877

Operation = Create, Verb = POST

Single item

SLIIT.com/students/

Multiple items

Same URL, items will be in the payload

Operation = Update, Verb = PUT

Collection

SLIIT.com/students/

Single item

SLIIT.com/students/IT123456

Multiple items

SLIIT.com/students/IT123456;IT456456;IT998877

Operation = Delete, Verb = DELETE

Collection

SLIIT.com/students/

Single item

SLIIT.com/students/IT123456

Multiple items

SLIIT.com/students/IT123456;IT456456;IT998877

Use MVC with REST and RESTful web services

Basic structure

RESTful web services JAX-RS

Ref : https://docs.oracle.com/javaee/6/tutorial/doc/gilik.html

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Server side development 1 – SOAP

Introduction to the web services

Web services are server-side application components, which provides a set of services.

The services of the web service are exposed via API.

An API is a set of functions and procedures allowing the creation of applications that access the features or data of an operating system, application or other service.

Multiple types of clients can communicate with the web service via the API.

Web services vs. Web Applications

WSDL

WSDL stands for Web Services Description Language. It is the standard format for describing a web service. WSDL was developed jointly by Microsoft and IBM. 

Features of WSDL 

WSDL is an XML based protocol for information exchange in decentralized and distributed environments.

WSDL definitions describe how to access a web service and what operations it will perform.

WSDL is a language for describing how to interface with XML based services.

WSDL is and integral part of Universal Description, Discovery and Integration (UDDI), an XML based worldwide business registry.

 WSDL is the language that UDDI uses

WSDL Usage 

WSDL is often used in combination with SOAP and XML schema to provide web services over the internet. A client program connecting to a web service can read the WSDL to determine what functions are available on the server. Any special data types used are embedded in the WSDL file in the form of XML schema. The client can then use SOAP to actually call one of the functions listed in the WSDL.

Ref:   https://www.tutorialspoint.com/wsdl/wsdl_introduction.htm

Specifies three fundamental properties:

1. What a service does – Operations (methods) provided by the service.

2. How a service is accessed – Data format and protocol details.

3. Where a service is located – Address (URL) details.

The document written in WSDL is also simply called a WSDL (or WSDL document).

The service provides the WSDL document and the web service client uses the WSDL document to create the stub (or to dynamically decode the message).

Stub

A stub is a small program routine that substitutes for a longer program, possibly to be loaded later or that is located remotely. For example, a program that uses Remote Procedure Calls (RPC ) is compiled with stubs that substitute for the program that provides a requested procedure.

The stub accepts the request and then forwards it (through another program) to the remote procedure. When that procedure has completed its service, it returns the results or other status to the stub which passes it back to the program that made the request.

Ref:  https://whatis.techtarget.com/definition/stub

WSDL Elements – Type 

Use the XML schema language to declare complex data types and elements that are used elsewhere in the WSDL document.

Serve as a container for defining any data types that are not described by the XML schema built-in types.

WSDL Elements – Message 

Any WSDL interface is a set of messages that the service behind the interface expects to send and receive.

 Messages are abstraction of request and response messages that client and web services exchange.

Messages are constructed from a number of XML schema typed part elements.

Ex:

<message name="getQuoteResponse">

          <part name="Result" type="xsd:float"/>

</message>

WSDL Elements – Port type 

Define web service functionality at abstract level, grouping sets of message exchanges into operations.

Contain a set of operations that incorporates input, output and fault messages and parameter order.

portType element may have one or more operation elements, each of which defines an RPC style or document style web service method.

WSDL Elements – Binding 

Map a portType to a specific protocol, typically SOAP over HTTP, using a specific data encoding style.

One portType can be bound to several different protocols by using more that one port.

Binding style may be either RPC or Document (SOAP)

WSDL Elements – Service 

It binds the web service to a specific network addressable location

Contain one or more port elements.

Access point for each port        

               - portType – The operations performed by the web service.

    ��          - message – The message used by the web service.

               - types – The data types used by the web service.

               - binding – The communication protocols used by the web service.

SOAP

SOAP stands for Simple Object Access Protocol.

SOAP supports both functional oriented and message oriented communication.

SOAP messages are carried as the payloads of some other network protocols.

(EX: HTTP or SMTP or FTP or TCP/IP)

Web services use SOAP as the logical transport mechanism for moving messages between services described by WSDL interfaces.

SOAP combines the data capabilities of XML with the transport capability of HTTP.

SOAP Messaging Modes 

RPC/ Literal                             Document/ Literal

RPC/ Encoded                         Document/ Encoded

SOAP Messaging 

Consistent envelope – Header and body

Consistent data encoding – Based on XML schema type system

Protocol binding framework

SOAP messages have encoding rules:

           Defines a serialization mechanism that can be used to exchange instance of application- defined objects.

SOAP Elements – Envelope 

Wraps entire message and contain header and body.

Defines an overall framework for expressing what is in a message, who should deal with it and whether it is optional or mandatory.

Envelope is a root XML element.

This tag indicates the start and end of the message to the receiver.

SOAP Elements – Header 

An optional element with additional information.

If the header is presented in the message, it must be the immediate child of envelope element.

Header adds meta-data about the content of a SOAP message and extends it with extra information.

Headers may be processed independently of the body.

SOAP Elements – Body

Application- specific message content being communicated as arbitrary XML payloads in the request and response messages.

Fault elements provides information about errors.

This is the only mandatory part of the envelope. Contains the actual message sent for the final recipient

SOAP Elements – Fault 

SOAP message that contains a fault element in the body is called a fault message.

SOAP faults are returned to the receiver’s immediate sender.

SOAP Elements – AttachmentPart 

SOAP messages may have one or more attachments.

Each AttachmentPart object has a MIME header to indicate the type of data it contains.

MIME (Multipurpose Internet Main Extension) is an internet standard that extends the format of email to support 

              -   Text in character sets other that ASCII.

              -  Non text attachments: audio, video, images, application programs

              -  Message bodies with multiple parts

              -  Header information is non-ASCII character sets

Ref:  https://en.m.wikipedia.org/wiki/MIME

Frameworks for SOAP web service development environments 

Apache CXF – Java

CodeIgniter – PHP

gSOAP – C and C++

Apache Axis – Java

Jello Framework – GAE/Java

.NET Framework – C#, VB.NET

Implement SOAP services

JAX-WS (Java API for XML Web Services) is a java package/ library for developing web services.

It supports both functional oriented and message-oriented communication via SOAP.

JAX-WS uses the javax.jws package and it uses annotations.

(Ex: @WebService, @WebMethod, @Oneway etc…)

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Distributed Systems

Introduction to Distributed Systems

There are two types of computer based systems, according to the distribution of the components.

Standalone systems (Desktop applications)

Distributed systems

Distributed Computing :

               Distributed computing is where multiple computing units are connected to achieve a common task.

Distributed systems :

               Distributed system consists of a collection of autonomous computers, connected through a network and distribution middleware.

Elements of distributed system

Processing components

Data networks

Data stores and data 

Configuration of above elements 

Advantages of Distributed Systems

All the nodes in the distributed system are connected to each other. So nodes can easily share data with other nodes

More nodes can easily be added to the distributed system

Failure of one node does not lead to the failure of the entire distributed system. Other nodes can still communicate with each other

Disadvantages of Distributed Systems

It is difficult to provide adequate security in distributed systems because the nodes as well as the connections need to be secured 

Some messages and data can be lost in the network while moving from one node to another 

The database connected to the distributed systems is quite complicated and difficult to handle as compared to a single user system 

Overloading may occur in the network if all the nodes of the distributed system try to send data at once 

Types of services in distributed systems

Mail service (SMTP, POP)

File transferring and sharing (FTP)

Remote logging (telnet)

Games and multimedia (RTP,SIP)

Web(HTTP)

Types of systems

Web sites

Web applications 

Web services and client apps 

Rich Internet Applications(RIAs)/ Rich Web based Applications (RiWAs)

Architecture of Distributed Systems

The basic architecture is client-server architecture (two-tier architecture)

The client sends a request asking the server for some service and the server responses with the resources.

The application is modeled as a set of services that are provided by servers and a set of clients that use these services

Clients know of servers but servers need not know of clients

Clients and servers are logical processes

Three-tier architecture is used, when data is needed and also to separate application logic of data

In a three-tier architecture, each of the application architecture layers may execute on a separate processor 

When further separation and distribution of components is needed, more layers can be added and extend the 2-tier or 3-tier architecture into a n-tier architecture 

Service oriented architecture

Distributed systems use Service Oriented Architecture (SOA) to communicate and share their services forming enterprise level services. 

These different systems may 

provide different services

are developed using different technologies 

communicate via the Enterprise Service Bus (ESB)

Enterprise Service Bus (ESB)

An Enterprise Service Bus (ESB) is fundamentally an architecture. It is a set of rules and principles for integrating numerous applications together over a bus-like infrastructure. ESB products enable users to build this type of architecture, but vary in the way that they do it and the capabilities that they offer. The core concept of the ESB architecture is that you integrate different applications by putting a communication bus between them and then enable each application to talk to the bus. This decouples systems from each other, allowing them to communicate without dependency on or knowledge of other systems on the bus. The concept of ESB was born out of the need to move away from point-to-point integration, which becomes brittle and hard to manage over time.

https://www.mulesoft.com/resources/esb/what-esb

Modularizing styles

Monolithic vs. Microservices

Monolithic  architecture

A monolithic architecture is the traditional unified model for the design of a software program.Monolithic, in this context, means composed all in one piece. Monolithic software is designed to be self-contained; components of the program are interconnected and interdependent rather than loosely coupled as is the case with modular software programs

Micro service architecture

Micro service architecture, or simply micro services, is a distinctive method of developing software systems that tries to focus on building single-function modules with well-defined interfaces and operations.

The trend has grown popular in recent years as Enterprises look to become more Agile and move towards a DevOps and continuous testing. Micro services can help create scalable, testable software that can be delivered weekly, not yearly.

https://smartbear.com/learn/api-design/what-are-microservices/

Communication in Distributed Systems

Communication techniques/technologies

Functional oriented communication

RPC/RMI

CORBA 

Message oriented communication 

SOAP

Resource oriented communication

REST

Data formatting/structuring

Plain text

Files (text, images)

Query String

XML

JSON

XML

XML is designed to store and transport data  and both human and machine readable.

The main and the only component of the XML is an Element.

An element has 3 components

Start tag

Body 

End tag 

An element has a name. 

Elements name are case sensitive and must start with a letter or underscore

Element names can contain letters, digits, hyphens, underscores and periods 

Element names cannot contain names 

Etc.

XML vs. JSON

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Industry Practices and Tools 2

Code quality

Importance of code quality

The long-term usefulness and long-term maintainability of the code

Minimize errors and easily debugged 

Improve understandability 

Decrease risks

Impact of code quality

Clarity

Maintainable

Documented 

Re-factored 

Well-tested 

Efficiency

Extensible

The quality of the code can be measured by different aspects

Weighted Micro Function Points (WMFP)

Weighted Micro Function Points is a modern software sizing algorithm invented by Logical Solutionsin 2009 which is a successor to solid ancestor scientific methods as COCOMO, COSYSMO, maintainability index, cyclomatic complexity, function points, and Halstead complexity.

It produces more accurate results than traditional software sizing methodologies while requiring less configuration and knowledge from the end user, as most of the estimation is based on automatic measurements of an existing source code. 

As many ancestor measurement methods use source lines of code (SLOC) to measure software size, WMFP uses a parser to understand the source code breaking it down into micro functions and derive several code complexity and volume metrics, which are then dynamically interpolated into a final effort score.

Halstead complexity measures 

Halstead complexity measures are software metrics introduced by Maurice Howard Halstead in 1977 as part of his treatise on establishing an empirical science of software development. 

Halstead made the observation that metrics of the software should reflect the implementation or expression of algorithms in different languages, but be independent of their execution on a specific platform. These metrics are therefore computed statically from the code. 

Halstead's goal was to identify measurable properties of software, and the relations between them.

Cyclomatic complexity

Cyclomatic complexity is a software metric used to indicate the complexity of a program. It is a quantitative measure of the number of linearly independent paths through a program's source code. 

Cyclomatic complexity is computed using the control flow graph of the program: the nodes of the graph correspond to indivisible groups of commands of a program, and a directed edge connects two nodes if the second command might be executed immediately after the first command. Cyclomatic complexity may also be applied to individual functions, modules, methods or classes within a program.

Dependency/Package management

Software project may have a backbone framework and many external artefacts linked.

These external artefacts may introduce many integration issues.

There are tools to manage these external artefacts towards minimizing these issues.

Composer (PHP)

Maven (Java) 

NPM(Node Package Manager)(JS)

Manage packages with Maven

Maven is a multi-purpose tool 

        ~  It makes the build process easy and provide a uniform build system

        ~  It provides quality project information

        ~  It allows transparent migration to new features

Maven is not only a dependency or package management tool, but also it is a build tool.

Role of package manager

A package manager deals with packages, distributions of software and data in archive files. Packages contain metadata, such as the software's name, description of its purpose, version number, vendor, checksum, and a list of dependencies necessary for the software to run properly. Upon installation, metadata is stored in a local package database. Package managers typically maintain a database of software dependencies and version information to prevent software mismatches and missing prerequisites. They work closely with software repositories, binary repository managers, and app stores. 

Use of the repositories

A repository in Maven holds build artifacts and dependencies of varying types.

There are exactly two types of repositories:

Local

Remote.

                 - Internal – Within the company

                 - External – via the internet, from the original repo.

The local repository is a directory on the computer where Maven runs. It caches remote downloads and contains temporary build artifacts that you have not yet released.

When using Maven, particularly in a corporate environment, connecting to the internet to download dependencies is not acceptable for security, speed or bandwidth reasons. For that reason, it is desirable to set up an internal repository to house a copy of artifacts, and to publish private artifacts to.

Repository manager purpose

Act as dedicated proxy server for public Maven repositories

Provide repositories as a deployment destination for your Maven project outputs 

Benefits and features

Significantly reduced number of downloads off remote repositories, saving time and bandwidth resulting in increased build performance

Improved build stability due to reduced reliance on external repositories 

Increased performance for interaction with remote SNAPSHOT repositories 

Potential for control of consumed and provided artifacts 

Creates a central storage and access to artifacts and meta data about them exposing build outputs to consumer such as other projects and developers, but also QA or operations teams or even customers 

Provides an effective platform for exchanging binary artifacts within your organization and beyond without the need for building artifact from source

Use the POM

Project Object Model (POM) is an XML representation of a Maven project held in a file named pom.xml

Contains the configurations of the project 

Developers involved and the roles they play

The defect tracking system

The organization and licenses

The URL of where the project lives 

The project's dependencies 

Build tools

Build tools are programs that automate the creation of executable applications from source code. 

(Ant/Ivy, Maven, Gradle, Sbt, MSBuild)

Build automation

On-demand automation

              A user running a script in the command line

Scheduled automation

    A continuous integration server running a nightly build.

Triggered automation

              A continuous integration server running a build on every commit to version control system

Role of build automation    

Automating the creation of a software build and the associated processes including, compiling computer source code into binary code, packaging binary code and running automated tests. 

Maven uses Convention over Configuration, 

                   which means developers are not required to create build process themselves.Developers do not have to mention each and every configuration detail.

Maven build life cycle

A Build Lifecycle is a well-defined sequence of phases, which define the order in which the goals are to be executed

The default life cycle of Maven uses 23 phases to build the application.

Maven build profile

A Build profile is a set of configuration values, which can be used to set or override default values of Maven build.

Additional tools and practices

Continuous integration

Continuous Integration (CI) is a development practice that requires developers to integrate code into a shared repository several times a day. Each check-in is then verified by an automated build, allowing teams to detect problems early. 

By integrating regularly, you can detect errors quickly, and locate them more easily. 

Configuration management

Configuration management (CM) is a systems engineering process for establishing and maintaining consistency of a product's performance, functional, and physical attributes with its requirements, design, and operational information throughout its life. 

Test automation

Automation testing is an Automatic technique where the tester writes scripts by own and uses suitable software to test the software. It is basically an automation process of a manual process.

The main goal of Automation testing is to increase the test efficiency and develop software value.

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Industry Practices and Tools 1

Version Controlling

Version control systems are a category of software tools that help a software team to manage changes to source code over time.

Version control software keeps track of every modification to the source in a special kind of database.

If a mistake is made

~       developers can turn back the clock

~       compare earlier versions of the code to help fix the mistake

~       minimizing disruption to all team members

Why VCS?

Collaboration

              ~  With a VCS, everybody on the team is able to work absolutely freely - on any file at any time.

Storing versions properly

              ~       A version control system acknowledges that there is only one project

Restoring previous versions

Understanding what happened

Back up

Models of VCS

GIT

GIT is the most commonly used version control system today and has quickly become the standard for version control.

Popular implementations:      

GitHub, GitLab, GitBucket, CloudForge

GIT Terminology

GIT File Status Life Cycle

GIT Commands

Content Delivery/Distributed Networks(CDN)

CDN is a geographically distributed network of proxy servers and their data centers.

The goal is to provide high availability and high performance by distributing the service spatially relative to end-users

Today, content delivery networks or CDNs have gained prominence. These are simply networked systems that are in cooperative mode and peak with neural networks.

Benefits

Improving web site load times

Reducing bandwidth costs

Increasing content availability and redundancy 

Improving web site security

Difference between web hosting servers and CDNs

Virtualization

Virtualization refers to the creation of a virtual resource such as a server, desktop, operating system, file, storage or network.

The main goal of virtualization is to manage workloads by radically transforming traditional computing to make it more scalable. Virtualization has been a part of the IT landscape for decades now, and today it can be applied to a wide range of system layers, including operating system-level virtualization, hardware-level virtualization and server virtualization.

Hardware virtualization  -   VMs, emulators

OS level virtualization (Desktop virtualization )

                -     Remote desktop terminals

Application level virtualization

                -     Runtimes (JRE/JVM, .NET), engines (games engines)

Containerization (also OS/application level )

                -     Dockers

 Other virtualization types  -   Database, network, storage

Pros and Cons of Virtualization

What is a Hypervisor in virtual machines?

A hypervisor is a process that separates a computer’s operating system and applications from the underlying physical hardware. Usually done as software although embedded hypervisors can be created for things like mobile devices.

The hypervisor drives the concept of virtualization by allowing the physical host machine to operate multiple virtual machines as guests to help maximize the effective use of computing resources such as memory, network bandwidth and CPU cycles.

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Programming Frameworks

Programming Paradigms

Programming paradigms classify programming languages based on their features and characteristics.

Ex: Functional programming, Object oriented programming

Some computer languages support multiple paradigms.

Ex: C++ support both functional OOP.

Non- structured programming

Earliest paradigm

A series of code

Becomes complex as the number of lines increases

Structured programming

Handle the issues of non structured programming by introducing the ways to structure the code using blocks.

               -  Control structures

               -  Functions/Procedures/Methods

               -  Classes/Blocks

Types of structured programming

               -  Block structured (functional) programming

               -  Object oriented programming

Event driven programming

Focus on the events launched outside the system.

               -  User events (Click, drag/drop)

               -  Schedulers/compilers

               -  Sensors, messages , hardware interrupts

Mostly related to the systems with GUIs.

Functional programming

Origins from Lambda Calculus.

Lambda Calculus : This is a formal system in mathematical logic for expressing computation based on function abstraction and application using variable binding and substitution.

No side – effects = Referential transparency

 Execution of a function does not effect on the global state of the system.

Use a declarative approach

Declarative approach : is a programming paradigm that expresses the logic of computation without describing its control flow.

This helps to minimize the side – effects.

Procedural programming

This paradigm helps to structure the code using blocks (procedures, routines, sub-routines, functions, methods).

 A procedure can implement a single algorithm using the control structures.

 Has side – effects.

 Use imperative approach.

Imperative approach : is a programming paradigm that uses statements to change program’s state.

Software Runtime Architecture

Languages can be categorized to the way they are processed and executed.

The general software runtime architecture

The communication between the application and the OS

needs additional components.

Compiled languages

Some executables can directly run on the OS.

Some uses virtual runtime machines.

Scripting languages

Source code is not compiled, it is directly executed and at the execution time the code is interpreted by a runtime machine.

Markup languages

No execution process for the markup languages.

The tools who have the knowledge to understand the markup languages can generate the output.

Development tools

Computer Aided Software Engineering (CASE) tools are used throughout the engineering life cycle of the software systems.

CASE software types

Individual tools – for specific task

Workbenches – multiple tools are combined focusing on a specific part of SDLC.

Environments – Combines many tools to support many activities throughout the SDLC.

Frameworks vs Plugins vs Libraries

Frameworks are concrete

A framework is incomplete

Framework helps solving recurring problems

The difference between JDK and JRE

JRE

JRE is an acronym for Java Runtime Environment. It is also written as Java RTE. The Java Runtime Environment is a set of software tools which are used for developing Java applications. It is used to provide the runtime environment. It is the implementation of JVM (Java Virtual Machine). It physically exists. It contains a set of libraries + other files that JVM uses at runtime.

JDK

JDK is an acronym for Java Development Kit. The Java Development Kit (JDK) is a software development environment which is used to develop Java applications and HYPERLINK applets. It physically exists. It contains JRE + development tools.

JDK is an implementation of any one of the below given Java Platforms released by Oracle Corporation:

Standard Edition Java Platform

Enterprise Edition Java Platform

Micro Edition Java Platform 

The JDK contains a private Java Virtual Machine (JVM) and a few other resources such as an interpreter/loader (java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc), etc. to complete the development of a Java Application.

JVM

JVM (Java Virtual Machine) is an abstract machine. It is called a virtual machine because it doesn't physically exist. It is a specification that provides a runtime environment in which Java bytecode can be executed. It can also run those programs which are written in other languages and compiled to Java bytecode.

The JVM performs the following main tasks:

Loads code

Verifies code

Executes code

Provides runtime environment

JDK = JRE + Development tools

JRE = JVM  + Library classes

Why we have to edit the path after installing the JDK?

When you type any thing in Command prompt , except the standard keywords like ( cd , dir) , the command prompt searches them in the folder where you are and tries to execute it , also as the cmd ( Command Prompt ) is from C:\WINDOWS\SYSTEM32 , so all the programs from here are accessible form anywhere in windows , also this is necessary , here , this is a necessity for windows to keep them in hand , whenever needed , where ever needed .

The path points to the location of the jre i.e. the java binary files such as the jvm and necessary libraries. The classpath points to the classes you developed so that the jvm can find them and load them when you run your product.

So essentially you need the path to find java so it can then find your classes and run them from the classpath.

Why you should need to set JAVA_HOME?

When you run a Java program you need to first start the JVM, typically this is done by running an executable, on Windows this is java.exe. You can get that in lots of ways for example just giving a full path:

C:\somedir\bin\java.exe

or may having it on your PATH.

You specify as command line arguments some class files or Jar files containing class files which are your program. But that's not enough, the java.exe itself needs various other resources, not least all the Java libraries. By setting the environment variable JAVA_HOME you specify where the JRE, and hence all those runtime resources, are to be found. You should ensure that the particular Java you execute matches the setting of JAVA_HOME.

Difference between PATH and JAVA HOME

Java IDE’s and comparisons

Eclipse

Eclips is  an open source platform. This is used in both open source and commercial projects. Starting in a humble manner, this has now emerged as a major platform, which is also used in several other languages.

The greatest advantage of Eclipse is that it features a whole plethora of plugins, which makes it versatile and highly customizable. This platform works for you in the background, compiling code, and showing up errors as they occur. The entire IDE is organized in Perspectives, which are essentially sort of visual containers, which offer a set of views and editors.

Eclipse’s multitasking, filtering and debugging are yet other pluses. Designed to fit the needs of large development projects, it can handle various tasks such as analysis and design, product management, implementation, content development, testing, and documentation as well.

NetBeans

NetBeans was independently developed and it emerged as an open source platform after it was acquired by Sun in 1999. This IDE can be used to develop software for all versions of Java ranging from Java ME up to the Enterprise Edition.

NetBeans offers you various different bundles – 2 C/C++ and PHP editions, a Java SE edition, the Java EE edition, and 1 kitchen sink edition that offers everything you will ever need for your project. This IDE also offers tools and editors which can be used for HTML, PHP, XML, JavaScript and more. You can now find support for HTML5 and other Web technologies as well.

NetBeans scores over Eclipse in that it features database support, with drivers for Java DB, MySQL, PostgreSQL, and Oracle. Its Database Explorer enables you to easily create, modify and delete tables and databases within the IDE.

IntelliJ Idea

IntelliJ offers support for a variety of languages, including Java, Scala, Groovy, Clojure and more. This IDE comes with features such as smart code completion, code analysis, and advanced refactoring. The commercial “Ultimate” version, which mainly targets the ​enterprise sector, additionally supports SQL, ActionScript, Ruby, Python, and PHP. Version 12 of this platform also comes with a new Android UI designer for Android app development.

IntelliJ too features several user-written plugins. It currently offers over 900 plugins, plus an additional 50+ in its enterprise version.

Conclusion

All of the above IDEs come with their own advantages. While Eclipse is still the widest used IDE, NetBeans is now gaining popularity with independent developers. While the enterprise edition of IntelliJ works like a marvel, some developers may consider it an unnecessary expense.