COMP3241 E-Business Technologies Richard Henson University of Worcester October 2014

Week 3 – Evolution of Web Apps, and Database connectivity Objectives: Objectives:  Contrast between client-end applications and client-server applications  Explain the architecture of web-based database connection with server-scripting  Create a presentable, updateable shopping page using product data linked to a database

Flatfiles and Databases Many so-called databases are just lists of data organised according to “fields”  retrieval of search strings or numerical data can take a looonnnggg time Database proper logically links the data:  hierarchically  relationally  object-oriented Relational still popular mainly because of SQL

Relational Databases Tight data structure saved data can be rapidly located… Real advantage of a true relational database is that SQL can be used for read/write & query database operations BUT… has to be properly designed

Database Design (1) Same principles apply as with any other relational database management system (RDBMS)…  identify entities & attributes  produce entity relationship  define logic relationships between entities

Database Design (2)  Any RDBMS…  make sure data is fully normalised  create tables & links  SQL statements need to communicate with the data to: »extract data from specific fields in particular tables »put data into specific fields in particular tables Some “self-taught” dynamic web developers are unaware of all this... build the data round the processing often get it wrong

Evolution of Application - RDBMS connectivity Early days of web development … Early days of web development …  connection between application and relational database  hard coded  made available as an API (application program interface)  client application then written to use the proprietary API If more than one RDBMS needed? If more than one RDBMS needed?  several different APIs  each needed their own client application…  added further to the complexity of the task!

Linking server script code with any data source: goal

Linking Server Script code with a data source Stage 1: 2-way link needed with a relational database:  need relevant remote data access components for web server »components for IIS-based scripts downloaded from Microsoft (as MDAC)  “datasets” defined using a programming language & embedded SQL  connectivity link needed to remote database, including path to/on web server

ActiveX Next stage in evolution towards UDA... Next stage in evolution towards UDA...  made up of… »OLE Object Linking and Embedding… Object Linking and Embedding… »Combined with COM (VB source code) Common Object Model Common Object Model ActiveX Data Objects make up a series of modular components called ADO ActiveX Data Objects make up a series of modular components called ADO  used for “run-time” web applications  basis of.net controls

The Success of ActiveX? The Success of ActiveX ® ? V. successful Microsoft client-side invention… (first move away from VB) V. successful Microsoft client-side invention… (first move away from VB) Run-time code (became known as “controls”) Run-time code (became known as “controls”)  NO source code so can’t be embedded in HTML, but can be called from a HTML file »runs on any Browser (not interpreted…)  allows compiled (i.e. executable) code to talk to host applications  difficult to “hack” the code if source code not available Scripts compiled into executable versions so source language is irrelevant Scripts compiled into executable versions so source language is irrelevant

More about VB ActiveX Data Objects (ADO) Applied client-side ActiveX principles to server-side Applied client-side ActiveX principles to server-side Simplified writing client applications to access data sources through OLE DB providers Simplified writing client applications to access data sources through OLE DB providers Data sources could now include:  spreadsheets  graphics  web pages…

Microsoft Solution (2) OLE DB Application of OLE/ActiveX principles to connectivity between applications and databases Application of OLE/ActiveX principles to connectivity between applications and databases  to be more precise, relational database management systems! Interface specification that provides a layer of abstraction between: Interface specification that provides a layer of abstraction between:  a data provider e.g. relational DBMS  a data consumer e.g. business object or client application

Universal Data Access achieved!

System Connection to the Database using OLE DB Provided by Microsoft Data Access Components (MDAC)  easily downloaded: » us/download/details.aspx?id=5793http:// us/download/details.aspx?id=5793  covers wide range of databases  need most up-to-date version of MDAC (2.8 SP1) to work with latest database versions…

Use of MDAC with “path” Once the correct component(s) have been chosen…  logical 'connection' can be set up with the database – wherever it is on the Internet!  BUT… if OLE DB connection isn’t correct, scripts on web server can’t even link with, let alone interact with, a relational database “Database Path” must include:  a definition of where the database is  a few simple rules on how the database should be treated

Making a connection to a database on the web server Two systems still used:  ODBC – “legacy”.asp scripting (VB source code)  OLE DB –.aspx connectivity (usually C# code behind) Essential to get connectivity working correctly »RAD tools like Visual Studio very helpful in achieving this… Once connectivity achieved, server-script can use embedded SQL commands to link to and communicate smoothly with database tables

Local databases and Local web pages (why not?) Some Problems:  database took a long while to download  could be tampered with!  if database ran locally how could data be updated… prices changed? new products added?... without changing the programming?  not possible!  massive security risk in any case!

Early online shopping example : Came out of the early “wow, Java” revolution in web development Came out of the early “wow, Java” revolution in web development  Whole system (30kb) written in Java Script, runs on the client machine (!) Whole system (30kb) written in Java Script, runs on the client machine (!)  stores & presents product data  shows all the components and functionality expected of a shopping cart system  interfaces with merchant systems that can be used to handle online payment TAKE A LOOK!!! Or download and run it yourself TAKE A LOOK!!! Or download and run it yourself

Critical Look at Client-end “apps” Absolutely fantastic! Absolutely fantastic! Even better on a mobile… Even better on a mobile… BUT usually for entertainment only… BUT usually for entertainment only…  only small data sources, or infrequently changed data sources are used  usually “single user”

Whatever happened to “client only” web shopping? In an ideal (Internet) world everything would be able to run via the browser on the client machine. Result: In an ideal (Internet) world everything would be able to run via the browser on the client machine. Result:  faster  all data local  app more controlled The “Java+client-end HTML” model is fine… The “Java+client-end HTML” model is fine…  until you need to store and change data… securely!!

Applications requiring multi-client use & shared data Specific multi-use requirement: Specific multi-use requirement: – large, regularly updated centralised data store that needs to be accessed through many connections – database downloaded every time the application is to be used!  Conclusion: » client not powerful enough? » or enough storage capacity? » not sufficient bandwidth? » anyway, downloading databases can compromise security

Secure remote database used with local web page... Accepted solution for client-server web applications…  data held in a secure place  product data easily updated  database processing can happen at a powerful server

Demands of Applications based on centralised data storage! Typically… the database must be : Typically… the database must be :  secure  readily accessible from all clients  queried remotely  alterable only by specific persons Only achievable through a client-server model Only achievable through a client-server model

Server Scripts Run only on the web server Run only on the web server Very different from client-side embedded code... Very different from client-side embedded code... Only interact with client & HTML browser through a client-server model Only interact with client & HTML browser through a client-server model

How Server Scripts can Interact with Databases Contain embedded SQL code that can extract data from or send data to a database

How Server Scripts can Interact with Databases  Whenever a database is updated… » updated data picked up by server-script when it runs » updated data displayed on client

How Server Scripts can Interact with Databases  Whenever a browser form captures data… »data transferred directly to relevant server »then stored in specified database field(s)

How Server Scripts Interact with Databases Whenever database information needs to be presented:  database fields and records taken into server memory  data sent to local machine to be displayed within a HTML format

Popular Types of Server Script Embedded code with HTML:.asp.php Java Server Pages PERL Separated programming code:.cgi.aspx

ASP.NET Environment Principles of ActiveX applied to server side Controls contain “run-time” code include OLEDB connectivity work very quickly very difficult to hack (assembly language code)

Parameter Passing between Programs Essential to programming Coding can rapidly get quite complex… Essential in e-commerce for  product selection  passing data into a remote SQL query  sound horrendous? »you’ll be eased into this gently

Mechanism for variable passing between Dynamic Web Pages Use HTML “forms”..... with “GET” or “POST” HTML “GET” function:  parameter/s tagged on to the URL e.g. » GET /thetest.jsp?firstname=richard&password=holiday s&lastname=henson&action=transferbankfundswww.address  Can result in v. long URLs…

Variable Passing between Dynamic Web Pages Alternative: “POST”  within form definition...  e.g. POST /thetest.jsp firstname=richard&password=holiday s&lastname=henson&action=transfer bankfunds

And now for the practical… Thanks for listening!  And for next week:  pnet-creating-shopping-cart-example.html pnet-creating-shopping-cart-example.html