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COMP2121 Internet Technology

COMP2121 Internet Technology. Richard Henson April 2011. Week 10: Running Dynamic Web pages. Objectives Explain briefly how the .net framework uses programming code running on a web server Explain what .net controls controls are, and why they are so useful in server scripting.

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COMP2121 Internet Technology

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  1. COMP2121Internet Technology Richard Henson April 2011

  2. Week 10: Running Dynamic Web pages • Objectives • Explain briefly how the .net framework uses programming code running on a web server • Explain what .net controls controls are, and why they are so useful in server scripting

  3. Advantages of using ASP.NET scripts • Asp.net code: • is compiled, not interpreted • v1 relied on an additional /bin folder for deployed “assemblies” or “controls” containing executable code • v2 onwards used /app_code folder – latter more flexible; could be referred to directly from a site configuration file • uses xml-type tags • can be written using a variety of programming languages • language declared at beginning of file • is full object-oriented and can easily be used as “controls” to respond to on-screen “events”

  4. Running controls with ASP.NET • Microsoft developed an “intermediate language” (IL) for .net framework • could be readily converted into machine code but the IL not easily hacked • Source code for .net development can be written in any language that can be translated into IL • VB.NET built on existing practice from asp • C# has proved to be most popular with developers, many of whom had previously used “C” and C++ • why use VB.net, when you can use C…?

  5. Components of the evolving .net framework • Evolving? • now at version v4.0 • .net common language infrastructure (CLI) • “managed execution” framework for scripts on an IIS web server • runs Intel x86 IL (Intermediate Language) code • Common Language run-time (CLR) for executing controls • ready to run • development language irrelevant

  6. Components of the evolving .net framework • /App_Data folder for database, web applications also must have a web.config file in the application root folder • As well as app_data folder, .net apps from v2 onwards also support the following additional folders: • app_code for“assemblies” (compiled code) & executables • app_browsers, app_themes, app_localresources, app_globalresources, app_webreferences…

  7. How the .net environment manages an application • “Assemblies” from .aspx files added to /app_code folder • CLI executes IL assemblies as CLR (runtime) • just a set of Win32 DLLs (dynamic link library files) created by compiling the assembly components • written in IL • makes sure script execution is “controlled” and kept within memory boundaries • loaded implicitly when a .net application is run

  8. Mechanism of Loading Assemblies for processing • “AppDomain” sets up a security boundary in memory for each application • Code (.exe, or .dll) loaded into process “spaceperfo” • JIT (Just in Time) compilation ensures “flat out performance” of the application… • cf Wallace & Grommit – latter lays out the track as the train is about to pass along it

  9. HTTP processing • Whole .net architecture designed “with failure in mind” • overall control with http.sys process • if memory usage gets too large… • whole .net framework pulled down and restarted… • Each AppDomain uses a pipeline of objects to handle requests • Httpapplication – oversees flow • Httpcontext – tracks “per request” state • Modules – generic “pluggable services • Handlers – http requests • Covers most (all?) eventualities and makes sure requests are correctly dealt with – no muddling of threads (!)

  10. Very Useful ASP.net components: 1. Web Controls • Reusable classes used to render parts of a page • Similar to Windows “forms” • New control created for each request • view state/Event tracking handled automatically • A typical web page may have a hierarchical structure of web controls to makes them easily manageable

  11. Very Useful ASP.net components: 2. Event Handlers • HTTP is stateless (no data retention) • no multi-step processes possible • e.g. HTML form contents disappear once form submitted • Web Controls provide scope for handling events, when triggered (or raised) • e.g. Page_Load, OnClick • “PostBack architecture” • allows web forms data to reappear on the screen

  12. Very Useful ASP.net components: 3. Master Pages & Themes • Master Page • resides in .master file • defines template for other pages • cf PowerPoint slide master • Contains top <html>, <body>, <form> tags • “Page” command utilises master either “static” or “dynamic” • “Page_init” process renders components • Themes • allow common styles to be applied across a series of pages • Developers can still use .CSS files • fully supported by the master file and page “themes” concepts

  13. .net Development and RAD tools • Don’t be phased by the .net architecture and use of a programming language like C… • the syntax of object-oriented C# is similar to Java • RAD tools such as Dreamweaver (earlier versions) and Visual Web Developer make development easy by… • providing a range of web controls already written in C# and ready to compile • helping with putting controls/assemblies into the /app_code folder • setting up the web.config file • many other previously written controls are available on the web

  14. Using Relational Databases • Real advantage of a true relational database is that SQL can be used for r/w & query database operations • so .net work with database involves AQL queries as well • As before, the RAD environment can use wizards to write the queries for you…

  15. Databases and the .net architecture • To make a two-way link between database and server scripts, it is just necessary to: • make relevant Microsoft data access components (MDAC) available … • define “datasets” (aspx) for the database using a programming language & embedded SQL • provide connectivity link to the database using the appropriate web control

  16. Microsoft Data Access Components (MDAC) • Provide connectivity between the system and a wide range of databases • Easily downloaded: • www.microsoft.com/data/download_21242023.htm • Just because a database type doesn’t seem to be represented, doesn’t mean that it can’t be… MDAC is regularly updated

  17. Database Design • Same principles apply as with any other relational database management system (RDBMS)… • identify entities & attributes • produce entity relationship • define logic relationships between entities • make sure data is fully normalised • create tables & links • use embedded SQL statements in the server script to communicate with the data: • extract data from specific fields in particular tables • put data into specific fields in particular tables • However, some “self-taught” developers will be unaware of this, and try to build the data round the processing…

  18. Evolution of connectivity between Applications & RDBMS • In the early web development days… • for the connection of an application to a relational databases… • a client application had to be written to use the proprietary API (application program interface) • Even then, there was a problem: • what if more than one RDBMS needs to be used? • The solution would be to use several different APIs (Application Programming Interfaces) • each needed a client application… • added greatly to the complexity of the task!

  19. The Microsoft Solution:the ODBC API • Aspiration: the “Universal Data Access” (UDA) model • all data consumers interact with all data providers… • response to the “API for each application” problem • First stage: ODBC = Open Database Connectivity • Developed in early 1990s: • common API for writing applications to access ANY relational DBMS for which an ODBC driver had been written • Once the APIs had all been written, tried, and tested… • any relational database with an ODBC compliant interface could use them • DSN model offered easy database path connectivity string management

  20. ActiveX • The next stage in evolution of Microsoft’s data objects model • sexy name for OLE v2.0 • made up of… • OLE • Object Linking and Embedding… • Combined with COM • Common Object Model • ActiveX Data Objects make up a series of modular components called ADO • used for “run-time” web applications • basis of .net controls

  21. More about ActiveX Data Objects (ADO) • Designed to simplify the writing of client applications to access data sources through OLE DB providers • more flexible than the earlier ODBC model • had to be specified on the local machine • limited to the data providers on that machine • Active X uses a common, easy-to-use object model • data sources can now also include: • spreadsheets • graphics • web pages

  22. OLE DB • Application of OLE/ActiveX principles to connectivity between applications and relational database management systems • interface specification provides a layer of abstraction between: • a data provider e.g. relational DBMS • a data consumer e.g. business object or client application

  23. Universal Data Access in practice

  24. Making a connection to a database on the web server • Each new version of .net provides more database controls • RAD tools very helpful at making these accessible… • server-script can then use SQL commands to link to and communicate smoothly with database tables • can save a lot of time…

  25. How FTP works • Used with TCP/IP to send files from one site (server) to another (client): • all Internet Servers have unique IP addresses • IP address used by IP protocol to manager transfer of data packets from one site to another • TCP used to arrange packets into the correct order, through listening on port 21 (as opposed to HTTP packets, which use port 80) • data rearranged into correct format for screen presentation by FTP protocol

  26. How FTP works • Server offers FTP as a web service • username/password controlled access to folders • tends to be associated with a www service • Device defined to be accessed through TCP port 21 • FTP service accessed by FTP clients via TCP/IP and the Internet

  27. FTP Servers • Set up (by default) to listen for FTP requests on TCP port 21 • During FTP access: • FTP client tools attempt to log on to the server, and get access to the directory or directories provided by the service • FTP client tool receives/sends selected files from/to appropriate directory on the FTP server • communication channel is terminated

  28. Windows FTP Servers • FTP service provided as a component of: • Internet Information Server (Microsoft) • Apache web server • Other third party products: • WS FTP server (Ipswitch) • FTP Serv-U

  29. Unix FTP servers • NOTE: to avoid upsetting Unix’s file system, filenames should be lower case and avoid punctuation • Examples: • ftpd (ftp daemon) – based on original DARPANet specification • Apache web server (originally for Unix)

  30. Thanks for listening… 

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