Introduction to the Web and .NET

Mark Sapossnek CS 594 Computer Science Department Metropolitan College Boston University

Prerequisites

   Basic computer skills Experience using the World Wide Web Experience developing object-oriented software

Learning Objectives

  Overview of Web and Internet technologies Review of existing Web programming technologies  Introduction to the .NET development platform

Agenda

   

Internet Technologies

Programming Languages and Paradigms Programming the Web .NET Overview

Internet Technologies

The World Wide Web

 A way to access and share information  Technical papers, marketing materials, recipes, ...

    A huge network of computers: the Internet Graphical, not just textual Information is linked to other information Application development platform    Shop from home Provide self-help applications for customers and partners ...

Internet Technologies

WWW Architecture Client Request:

http://www.msn.com/default.asp

Network PC/Mac/Unix + Browser TCP/IP Server Response:

…

Web Server

Internet Technologies

WWW Architecture

 Client/Server, Request/Response architecture    You request a Web page  e.g. http://www.msn.com/default.asp

 HTTP request The Web server responds with data in the form of a Web page  HTTP response  Web page is expressed as HTML Pages are identified as a Uniform Resource Locator (URL)     Protocol: http Web server: www.msn.com

Web page: default.asp

Can also provide parameters: ?name=Leon

Internet Technologies

Web Standards

 Internet Engineering Task Force (IETF)  http://www.ietf.org/  Founded 1986  Request For Comments (RFC) at http://www.ietf.org/rfc.html

 World Wide Web Consortium (W3C)  http://www.w3.org

 Founded 1994 by Tim Berners-Lee  Publishes technical reports and recommendations

Internet Technologies

Web Design Principles

  

Interoperability:

Web languages and protocols must be compatible with one another independent of hardware and software.

Evolution:

The Web must be able to accommodate future technologies. Encourages simplicity, modularity and extensibility.

Decentralization:

robustness. Facilitates scalability and

Internet Technologies

Hypertext Markup Language (HTML)

 The markup language used to represent Web pages for viewing by people  Designed to display data, not store/transfer data   Rendered and viewed in a Web browser Can contain

links

and other pages to images, documents,   Not extensible Derived from Standard Generalized Markup Language (SGML)  HTML 3.2, 4.01, XHTML 1.0

Internet Technologies

HTML Forms

 Enables you to create interactive user interface elements  Buttons  Text boxes  Drop down lists  Check boxes   User fills out the form and submits it Form data is sent to the Web server via HTTP when the form is submitted

Internet Technologies

Hypertext Transport Protocol (HTTP)

 The top-level protocol used to request and return data    E.g. HTML pages, GIFs, JPEGs, Microsoft Word documents, Adobe PDF documents, etc.

  Request/Response protocol Methods: GET , POST , HEAD , … HTTP 1.0: simple HTTP 1.1: more complex

Internet Technologies

HTTP Request Method File HTTP version Headers GET /default.asp HTTP/1.0

Accept: image/gif, image/x-bitmap, image/jpeg, */* Accept-Language: en User-Agent: Mozilla/1.22 (compatible; MSIE 2.0; Windows 95) Connection: Keep-Alive If-Modified-Since: Sunday, 17-Apr-96 04:32:58 GMT Blank line Data – none for GET

Internet Technologies

HTTP Response HTTP version Status code Reason phrase Headers HTTP/1.0 200 OK Date: Sun, 21 Apr 1996 02:20:42 GMT Server: Microsoft-Internet-Information-Server/5.0 Connection: keep-alive Content-Type: text/html Last-Modified: Thu, 18 Apr 1996 17:39:05 GMT Content-Length: 2543 Some data... blah, blah, blah Data

Internet Technologies

HTTP Server Status Codes Code

200 201 301 302 400 401 403 404 500

Description

OK Created Moved Permanently Moved Temporarily Bad Request – not understood Unauthorized Forbidden – not authorized Not Found Internal Server Error

Internet Technologies

HTTP

  HTTP is a stateless protocol Each HTTP request is independent of previous and subsequent requests   HTTP 1.1 introduced keep-alive applications are designed for efficiency Statelessness has a big impact on how scalable

Internet Technologies

Cookies

 A mechanism to store a small amount of information (up to 4KB) on the client     A cookie is associated with a specific web site Cookie is sent in HTTP header Cookie is sent with each HTTP request Can last for only one session (until browser is closed) or can persist across sessions  Can expire some time in the future

Internet Technologies

HTTPS

  A secure version of HTTP Allows client and server to exchange data with confidence that the data was neither modified nor intercepted  Uses Secure Sockets Layer (SSL)/ Transport Layer Security (TLS)

Internet Technologies

URIs, URLs and URNs

 Uniform Resource Identifier (URI = URL or URN)  Generic term for all textual names/addresses  Uniform Resource Locator (URL)  The set of URI schemes that have explicit instructions on how to access the resource over the Internet, e.g. http , ftp , gopher  Uniform Resource Name (URN) 1) A URI that has an institutional commitment to availability, etc.

2) A particular scheme intended to identify resources e.g.

urn:schemas:httpmail:subject

Internet Technologies

Multipurpose Internet Mail Extensions (MIME)

 Defines types of data/documents  text/plain   text/html image/gif  image/jpeg  audio/x-pn-realaudio  audio/x-ms-wma  video/x-ms-asf  application/octet-stream

Internet Technologies

MIME

   Specifies character sets, e.g. ASCII Supports multi-part messages Originally designed for email, but also used in other places, such as HTTP

Internet Technologies

Browsers

   Client-side application Requests HTML from Web server and renders it Popular browsers:  Netscape   Internet Explorer Opera  others  Also known as a User Agent

Internet Technologies

Clients & Servers

 Client and Server computers both have:  CPU   Memory I/O  Disks  Network  Bus   Multi-tasking operating system Applications

Internet Technologies

Clients & Servers

 Clients  Generally supports a single user  Optimized for responsiveness to user  User interface, graphics  Servers  Supports multiple users  Optimized for throughput   More: CPUs (SMP), memory, disks (SANs), I/O Provide services (e.g. Web, file, print, database, e-mail, fax, transaction, telnet, directory)

Internet Technologies

Proxy Servers & Firewalls

 Proxy Server  A server that sits between a client (running a browser) and the Internet   Improves performance by caching commonly used Web pages Can filter requests to prevent users from accessing certain Web sites  Firewall  A server that sits between a network and the Internet to prevent unauthorized access to the network from the Internet

Internet Technologies

Networks

 Network = an interconnected collection of independent computers   Why have networks?

    Resource sharing Reliability Cost savings Communication Web technologies add:    New business models: e-commerce, advertising Entertainment Applications without a client-side install

Internet Technologies

Networks

 Network scope  internet: a collection of connected networks  Internet: a specific world-wide network based on TCP/IP, used to connect companies, universities, governments, organizations and individuals. Originated as ARPANET, funded by the US DoD.

 intranet: a network based on Internet technologies that is internal to a company or organization  extranet: a network based on Internet technologies that connects one company or organization to another

Internet Technologies

Networks

 Network technology is largely determined by scale:  Local Area Network (LAN): Span up to a few kilometers. Bus vs. ring topologies  Wide Area Networks (WAN): Can span a country or continent. WANs use routers as intermediate nodes to connect transmission lines

Internet Technologies

Networks

 Network technology    Broadcasting  Packets of data are sent from one machine and received by all computers on the network  Multicast: packets are received by a subset of the machines on a network Point-to-point  Packets have to be routed from one machine to another; there many be many paths In general, geographically localized networks use broadcasting, while disperse networks use point-to-point

Internet Technologies

Networks OSI Model Layers Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer TCP/IP Protocol Architecture Layers Application Layer Host-to-Host Transport Layer Internet Layer Network Interface Layer Telnet FTP SMTP DNS RIP SNMP HTTP ARP Ethernet TCP Token Ring IP TCP/IP Protocol Suite Frame Relay UDP IGMP ICMP ATM

Internet Technologies

Network Protocol Stack HTTP TCP IP Ethernet HTTP TCP IP Ethernet

Internet Technologies

Networks - Internet Layer

  Internet Protocol (IP) Responsible for getting packets from source to destination across multiple hops   Not reliable IP address: 32 bit value usually written in dotted decimal notation as four 8-bit numbers (0 to 255); e.g. 130.50.12.4

Internet Technologies

Networks - Transport Layer

   Provides efficient, reliable and cost-effective service Uses the Sockets programming model Ports identify application  Well-known ports identify standard services (e.g. HTTP uses port 80, SMTP uses port 25)  Transmission Control Protocol (TCP)  Provides reliable, connection-oriented byte stream  UDP  Connectionless, unreliable

Internet Technologies

Networks - Application Layer

       Telnet: Remote sessions File Transfer Protocol (FTP) Network News Transfer Protocol (NNTP) Simple Network Management Protocol (SNMP) Simple Mail Transfer Protocol (SMTP) Post Office Protocol (POP3) Interactive Mail Access Protocol (IMAP)

Internet Technologies

Networks Domain Name System (DNS)

 Provides user-friendly domain names, e.g. www.msn.com  Hierarchical name space with limited root names     .com

.net

.gov

.edu

    .org

.mil

.jp

.de

 DNS servers map domain names to IP addresses

Internet Technologies

Extensible Markup Language (XML)

     Represents hierarchical data A meta-language: a language for defining other languages Extensible Useful for data exchange and transformation Simplified version of SGML

Agenda

    Internet Technologies

Programming Languages and Paradigms

Programming the Web .NET Overview

Programming Languages

   Machine code Assembly language High-level languages  Fortran, LISP, Cobol   C, Pascal, Basic, Smalltalk C++, Eiffel  Java, C#  Scripting languages  Shell scripts, Perl, TCL, Python, JavaScript, VBScript

Programming Paradigms

     Unstructured programming Structured programming Object-oriented programming Component-based programming Event-based programming

Programming Paradigms

Unstructured Programming

 See “Go To Statement Considered Harmful” at http://www.acm.org/classics/oct95/

Programming Paradigms

Structured Programming

  Sequence Conditional   if then else switch  Looping    for i from 1 to n do while do until   Functions Exceptions

Programming Paradigms

Object-Oriented Programming

 Objects have data and behavior  Data: members, fields, variables, slots, properties  Behavior: methods, functions, procedures  Using objects is easy  First instantiate the type of object desired  Then call its methods and get/set its properties  Designing new types of objects can be hard  Design goals often conflict: simplicity, functionality, reuse, performance

Programming Paradigms

Object-Oriented Programming

 Key object-oriented concepts  Identity        Encapsulation  Data + behavior  Information hiding (abstraction) Classes vs. instances Polymorphism Interfaces Delegation, aggregation Inheritance Patterns

Programming Paradigms

Component-Based Programming

 Components  Independent modules of reuse and deployment  Coarser-grained than objects (objects are language-level constructs)  Includes multiple classes  Often language-independent  In the general case, the component writer and the component user don’t know each other, don’t work for the same company, and don’t use the same language

Programming Paradigms

Component-Based Programming

 Component Object Model (COM)  Initial Microsoft standard for components  Specifies a protocol for instantiating and using components in-process, across processes or across machine boundaries   Basis for ActiveX, OLE, and many other technologies Can be created in Visual Basic, C++, .NET, …  Java Beans  Java standard for components  Not language-independent

Programming Paradigms

Event-Based Programming

 When something of interest occurs, an event is raised and application-specific code is executed  Events provide a way for you to hook in your own code into the operation of another system   Event = callback User interfaces are all about events  onClick , onMouseOver , onMouseMove …  Events can also be based upon time or interactions with the network, operating system, other applications, etc.

Agenda

    Internet Technologies Programming Languages and Paradigms

Programming the Web

.NET Overview

Programming the Web

Client-Side Code

 What is client-side code?

 Software that is downloaded from Web server to browser and then executes on the client  Why client-side code?

     Better scalability: less work done on server Better performance/user experience Create UI constructs not inherent in HTML  Drop-down and pull-out menus  Tabbed dialogs Cool effects, e.g. animation Data validation

Programming the Web

Client-Side Technologies

  DHTML/JavaScript COM  ActiveX controls  COM components  Remote Data Services (RDS)     Java Plug-ins Helpers Remote Scripting

Programming the Web

Dynamic HTML (DHTML)

  Script that is embedded within an HTML page Usually written in JavaScript (ECMAScript, JScript) for portability  Internet Explorer also supports VBScript and other scripting languages  Each HTML element becomes an object that has associated events (e.g. onClick )  Script provides code to respond to browser events

Programming the Web

DHTML

 The DHTML Document Object Model (DOM)

window event navigator history document location screen frames all location children forms selection body text password file radio checkbox button submit reset textarea select option links

Programming the Web

ActiveX

  Based on COM Native only to Internet Explorer  Supported in Netscape with a plug-in  Good when you know your users (e.g. intranet) or can specify which browser to use  Small, efficient code

Programming the Web

Java Applets

    Based on Java bytecode Held great promise as a portable, pain-free way to download client-side code:  “Write once, run anywhere” Fairly safe: code runs in a “sandbox” Compatibility and performance issues have prevented common usage

Programming the Web

Server-Side Code

 What is server-side code?

 Software that runs on the server, not the client    Receives input from  URL parameters  HTML form data  Cookies  HTTP headers Can access server-side databases, e-mail servers, files, mainframes, etc.

Dynamically builds a custom HTML response for a client

Programming the Web

Server-Side Code

 Why server-side code?

    Accessibility  You can reach the Internet from any browser, any device, any time, anywhere Manageability  Does not require distribution of application code  Easy to change code Security   Source code is not exposed Once user is authenticated, can only allow certain actions Scalability  Web-based 3-tier architecture can scale out

Programming the Web

Server-Side Technologies

        Common Gateway Interface (CGI) Internet Server API (ISAPI) Netscape Server API (NSAPI) Active Server Pages (ASP) Java Server Pages (JSP) Personal Home Page (PHP) Cold Fusion (CFM) ASP.NET

Programming the Web

Active Server Pages (ASP)

 Technology to easily create server-side applications  ASP pages are written in a scripting language, usually VBScript or JScript  An ASP page contains a sequence of static HTML interspersed with server-side code  ASP script commonly accesses and updates data in a database

Programming the Web

ASP HTTP request (form data, HTTP header data) HTTP response HTML, XML ASP page (static HTML, server-side logic)

Agenda

    Internet Technologies Programming Languages and Paradigms Programming the Web

.NET Overview

.NET Overview

        Introduction to .NET

Web Services The .NET Framework Common Language Runtime Windows Forms Web Forms ADO.NET

Languages

Introduction to .NET

What is .NET?

 A vision of how information technology will evolve   A platform that supports the vision A business model of software as a service

Introduction to .NET

What is .NET?

 A vision  Web sites will be joined by Web services    New smart devices will join the PC User interfaces will become more adaptable and customizable Enabled by Web standards

Introduction to .NET

What is .NET?

      A platform The .NET Framework Visual Studio.NET

}

The focus of this course

.NET Enterprise Servers  Database, Messaging, Integration, Commerce, Proxy, Security, Mobility, Orchestration, Content Management .NET Building Block Services   Passport .NET My Services (“Hailstorm”) Goal: make it incredibly easy to build powerful Web applications and Web services

Introduction to .NET

What is .NET?

    A business model Software as a service Subscription-based services Application hosting, e.g. bCentral

Introduction to .NET

The .NET Platform Clients Applications Protocols: HTTP, HTML, XML, SOAP, UDDI Web Form Web Service .NET Framework Windows Tools: Visual Studio.NET, Notepad Your Internal Web Service .NET Foundation Web Services Third-Party Web Services .NET Enterprise Servers

Web Services

 A programmable application component accessible via standard Web protocols    The center of the .NET architecture Exposes functionality over the Web Built on existing and emerging standards  HTTP, XML, SOAP, UDDI, WSDL, …

Web Services

Evolution of the Web HTML, XML HTML HTML Generation 1 Static HTML Generation 2 Web Applications Generation 3 Web Services HTML, XML

The .NET Framework

What Is the .NET Framework?

     A set of technologies for developing and using components to create: Web Forms Web Services Windows Applications     Supports the software lifecycle Development Debugging Deployment Maintenance

The .NET Framework

The .NET Framework and Visual Studio.NET

VB C++ C# JScript … Common Language Specification ASP.NET: Web Services and Web Forms Windows Forms ADO.NET: Data and XML .NET Framework Base Classes Common Language Runtime

The .NET Framework

.NET Framework Classes Services Description Discovery Protocols System.Web

UI HtmlControls WebControls Caching Configuration Security SessionState OLEDB Design System.Data

Collections Configuration Diagnostics Globalization SQL SQLTypes IO Net Reflection Resources Form System.Windows.Forms

MessageBox Button ListControl System.Drawing

Drawing2D Imaging Printing Text XSLT XPath System.Xml

Serialization System Security ServiceProcess Text Threading Runtime InteropServices Remoting Serialization

Common Language Runtime

Goals

 Development services   Deep cross-language interoperability Increased productivity  Deployment services   Simple, reliable deployment Fewer versioning problems –

NO MORE ‘DLL HELL’

 Run-time services    Performance Scalability Availability    Reliability Security Safety

Common Language Runtime

Compilation Source Code C++, C#, VB or any .NET language Compiler csc.exe or vbc.exe

Assembly DLL or EXE

Common Language Runtime

Assemblies

     Assembly Logical unit of deployment Contains Manifest, Metadata, MSIL and resources  Manifest Metadata about the components in an assembly (version, types, dependencies, etc.)  Type Metadata Completely describes all types defined in an assembly: properties, methods, arguments, return values, attributes, base classes, …

Common Language Runtime

Assemblies

 Microsoft Intermediate Language (MSIL, IL)  All languages compile to IL (managed code)  IL is always compiled to native code before being executed  Resources  E.g. .bmp, .jpg

Source code MSIL

Common Language Runtime

Execution Model VB Compiler Assembly C# Compiler Assembly C++ Compiler Assembly Common Language Runtime JIT Compiler Ngen Native code Managed Code CLR Services Managed Managed Code Operating System Services Unmanaged Code

Common Language Runtime

Services

       Code management Conversion of MSIL to native code Loading and execution of managed code Creation and management of metadata Verification of type safety Insertion and execution of security checks Memory management and isolation  Handling exceptions across languages  Interoperation between .NET Framework objects and COM objects and Win32 DLLs  Automation of object layout for late binding  Developer services (profiling, debugging, etc.)

Common Language Runtime

Multiple Language Support

    Common Type System (CTS) A superset of the data types used by most modern programming languages  Common Language Specification (CLS) A subset of CTS that allows code written in different languages to interoperate   What languages?

Microsoft: C++, Visual Basic, C#, JScript Third-Party: Cobol, Eiffel, Smalltalk, Scheme, Oberon, Haskell, Java, Python, Perl, …

Common Language Runtime

Applications

  An application consists of one or more assemblies How does one assembly bind to another?

 Based upon metadata and policy   Local (preferred) Assembly Global Cache  Multiple versions of an assembly may exist on the same machine  Easier software deployment, updates and removal  Multiple versions of an assembly can even be used by the same application

Common Language Runtime

Security

    Evidence-based security (authentication) Based on user identity and code identity Configurable policies Imperative and declarative interfaces

Windows Forms

     Framework for building rich clients  Built upon .NET Framework, languages  Rapid Application Development (RAD) Visual inheritance Anchoring and docking Rich set of controls Extensible controls   Data-aware Easily hooked into Web Services     ActiveX support Licensing support Printing support Advanced graphics

Web Forms

 Built with ASP.NET

 Logical evolution of ASP  Similar development model: edit the page and go   Requires less code New programming model      Event-driven/server-side controls Rich controls (e.g. data grid, validation) Data binding Controls generate browser-specific code Simplified handling of page state

Web Forms

  Allows separation of UI and business logic Uses .NET languages  Not just scripting    Easy to use components XCOPY/FTP deployment Simple configuration (XML-based)

Web Forms

  Caching (pages, fragments, custom) Scalable session state management   Tracing support ASP.NET is extensible   No ISAPI / ASP dichotomy  Automatic process rollover Forms-based authentication

ADO.NET

      Similar to ADO, but better factored Language-neutral data access Supports two styles of data access   Disconnected Forward-only, read-only access Supports data binding DataSet: a collection of tables Can view and process data relationally (tables) or hierarchically (XML)

Languages

C #

   New language created for .NET

Safe, productive evolution of C++ Key concepts:  Component-oriented   Everything is an object Robust and durable code  Preserving your investment   Submitted to ECMA for standardization Uses .NET Framework classes

Languages

Visual Basic.NET

 Modernizes and simplifies Visual Basic  Inheritance  Threading  Exception handling   Support for late binding Uses .NET Framework classes

Conclusion

    Internet Technologies Programming Languages and Paradigms Programming the Web .NET Overview

More Resources

    HTTP   http://msdn.microsoft.com/library/periodic/period96/protocol.htm

HTTP Essentials

, Stephen Thomas, 2001, Wiley, ISBN 0471-39823-3 Cookies  http://msdn.microsoft.com/library/default.asp?URL=/library/partb ook/instantj/cookies.htm

MIME   http://www.ufaq.org/navcom/mime_tutorial.html

http://www.irvine.com/~mime/ Networks  http://msdn.microsoft.com/library/periodic/period99/ntp99b3.htm

More Resources

  XML  http://msdn.microsoft.com/xml/default.asp

  http://www.w3.org/XML/

Essential XML

, Don Box, Aaron Skonnard, John Lam, Addison Wesley, 2000, ISBN 0-201-70914-7 .NET

    http://www.microsoft.com/net/ http://msdn.microsoft.com/net/ http://www.gotdotnet.com

msnews.microsoft.com news server  microsoft.public.dotnet.general newsgroup