Introduction to the Web and NET Mark Sapossnek
Introduction to the Web and. NET Mark Sapossnek CS 594 Computer Science Department Metropolitan College Boston University
Prerequisites w Basic computer skills w Experience using the World Wide Web w Experience developing object-oriented software
Learning Objectives w Overview of Web and Internet technologies w Review of existing Web programming technologies w Introduction to the. NET development platform
Agenda w w Internet Technologies Programming Languages and Paradigms Programming the Web. NET Overview
Internet Technologies The World Wide Web w A way to access and share information n w w 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 n n n Shop from home Provide self-help applications for customers and partners. . .
Internet Technologies WWW Architecture PC/Mac/Unix + Browser Client Request: http: //www. msn. com/default. asp Network TCP/IP Response: <html>…</html> Server Web Server
Internet Technologies WWW Architecture w Client/Server, Request/Response architecture n You request a Web page l l n The Web server responds with data in the form of a Web page l l n e. g. http: //www. msn. com/default. asp HTTP request HTTP response Web page is expressed as HTML Pages are identified as a Uniform Resource Locator (URL) l l Protocol: http Web server: www. msn. com Web page: default. asp Can also provide parameters: ? name=Leon
Internet Technologies Web Standards w Internet Engineering Task Force (IETF) n n n http: //www. ietf. org/ Founded 1986 Request For Comments (RFC) at http: //www. ietf. org/rfc. html w World Wide Web Consortium (W 3 C) n n n http: //www. w 3. org Founded 1994 by Tim Berners-Lee Publishes technical reports and recommendations
Internet Technologies Web Design Principles w Interoperability: Web languages and protocols must be compatible with one another independent of hardware and software. w Evolution: The Web must be able to accommodate future technologies. Encourages simplicity, modularity and extensibility. w Decentralization: Facilitates scalability and robustness.
Internet Technologies Hypertext Markup Language (HTML) w The markup language used to represent Web pages for viewing by people n Designed to display data, not store/transfer data w Rendered and viewed in a Web browser w Can contain links to images, documents, and other pages w Not extensible w Derived from Standard Generalized Markup Language (SGML) w HTML 3. 2, 4. 01, XHTML 1. 0
Internet Technologies HTML Forms w Enables you to create interactive user interface elements n n Buttons Text boxes Drop down lists Check boxes w User fills out the form and submits it w Form data is sent to the Web server via HTTP when the form is submitted
Internet Technologies Hypertext Transport Protocol (HTTP) w The top-level protocol used to request and return data n w w 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 <HTML> Some data. . . blah, blah </HTML> Data
Internet Technologies HTTP Server Status Code Description 200 OK 201 Created 301 Moved Permanently 302 Moved Temporarily 400 Bad Request – not understood 401 Unauthorized 403 Forbidden – not authorized 404 Not Found 500 Internal Server Error
Internet Technologies HTTP w HTTP is a stateless protocol w Each HTTP request is independent of previous and subsequent requests w HTTP 1. 1 introduced keep-alive for efficiency w Statelessness has a big impact on how scalable applications are designed
Internet Technologies Cookies w A mechanism to store a small amount of information (up to 4 KB) on the client w A cookie is associated with a specific web site w Cookie is sent in HTTP header w Cookie is sent with each HTTP request w Can last for only one session (until browser is closed) or can persist across sessions w Can expire some time in the future
Internet Technologies HTTPS w A secure version of HTTP w Allows client and server to exchange data with confidence that the data was neither modified nor intercepted w Uses Secure Sockets Layer (SSL)/ Transport Layer Security (TLS)
Internet Technologies URIs, URLs and URNs w Uniform Resource Identifier (URI = URL or URN) n Generic term for all textual names/addresses w Uniform Resource Locator (URL) n The set of URI schemes that have explicit instructions on how to access the resource over the Internet, e. g. http, ftp, gopher w 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) w Defines types of data/documents n n n n text/plain text/html image/gif image/jpeg audio/x-pn-realaudio/x-ms-wma video/x-ms-asf application/octet-stream
Internet Technologies MIME w Specifies character sets, e. g. ASCII w Supports multi-part messages w Originally designed for email, but also used in other places, such as HTTP
Internet Technologies Browsers w Client-side application w Requests HTML from Web server and renders it w Popular browsers: n n Netscape Internet Explorer Opera others w Also known as a User Agent
Internet Technologies Clients & Servers w Client and Server computers both have: n n n CPU Memory I/O l l n n n Disks Network Bus Multi-tasking operating system Applications
Internet Technologies Clients & Servers w Clients n n n Generally supports a single user Optimized for responsiveness to user User interface, graphics w Servers n n 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 w Proxy Server n n n 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 w Firewall n A server that sits between a network and the Internet to prevent unauthorized access to the network from the Internet
Internet Technologies Networks w Network = an interconnected collection of independent computers w Why have networks? n n Resource sharing Reliability Cost savings Communication w Web technologies add: n n n New business models: e-commerce, advertising Entertainment Applications without a client-side install
Internet Technologies Networks w Network scope n n 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 Do. D. 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 w Network technology is largely determined by scale: n n 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 w Network technology n Broadcasting l l n Point-to-point l n 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 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 TCP/IP Protocol Suite Telnet FTP Host-to-Host Transport Layer SMTP DNS RIP TCP Internet Layer ARP Network Interface Layer Ethernet SNMP HTTP UDP IGMP IP Token Ring Frame Relay ICMP ATM
Internet Technologies Network Protocol Stack HTTP TCP IP IP Ethernet
Internet Technologies Networks - Internet Layer w Internet Protocol (IP) w Responsible for getting packets from source to destination across multiple hops w Not reliable w 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 w Provides efficient, reliable and cost-effective service w Uses the Sockets programming model w Ports identify application n Well-known ports identify standard services (e. g. HTTP uses port 80, SMTP uses port 25) w Transmission Control Protocol (TCP) n Provides reliable, connection-oriented byte stream w UDP n Connectionless, unreliable
Internet Technologies Networks - Application Layer w w w w 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 (POP 3) Interactive Mail Access Protocol (IMAP)
Internet Technologies Networks - Domain Name System (DNS) w Provides user-friendly domain names, e. g. www. msn. com w Hierarchical name space with limited root names n n . com. net. gov. edu n n . org. mil. jp. de w DNS servers map domain names to IP addresses
Internet Technologies Extensible Markup Language (XML) w Represents hierarchical data w A meta-language: a language for defining other languages w Extensible w Useful for data exchange and transformation w Simplified version of SGML
Agenda w w Internet Technologies Programming Languages and Paradigms Programming the Web. NET Overview
Programming Languages w Machine code w Assembly language w High-level languages n n Fortran, LISP, Cobol C, Pascal, Basic, Smalltalk C++, Eiffel Java, C# w Scripting languages n Shell scripts, Perl, TCL, Python, Java. Script, VBScript
Programming Paradigms w w w Unstructured programming Structured programming Object-oriented programming Component-based programming Event-based programming
Programming Paradigms Unstructured Programming w See “Go To Statement Considered Harmful” at http: //www. acm. org/classics/oct 95/
Programming Paradigms Structured Programming w Sequence w Conditional n n if then else switch w Looping n n n for i from 1 to n do while do until w Functions w Exceptions
Programming Paradigms Object-Oriented Programming w Objects have data and behavior n n Data: members, fields, variables, slots, properties Behavior: methods, functions, procedures w Using objects is easy n n First instantiate the type of object desired Then call its methods and get/set its properties w Designing new types of objects can be hard n Design goals often conflict: simplicity, functionality, reuse, performance
Programming Paradigms Object-Oriented Programming w Key object-oriented concepts n n Identity Encapsulation l l n n n Data + behavior Information hiding (abstraction) Classes vs. instances Polymorphism Interfaces Delegation, aggregation Inheritance Patterns
Programming Paradigms Component-Based Programming w Components n n Independent modules of reuse and deployment Coarser-grained than objects (objects are language-level constructs) Includes multiple classes Often language-independent w 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 w Component Object Model (COM) n n Initial Microsoft standard for components Specifies a protocol for instantiating and using components in-process, across processes or across machine boundaries Basis for Active. X, OLE, and many other technologies Can be created in Visual Basic, C++, . NET, … w Java Beans n n Java standard for components Not language-independent
Programming Paradigms Event-Based Programming w When something of interest occurs, an event is raised and application-specific code is executed w Events provide a way for you to hook in your own code into the operation of another system w Event = callback w User interfaces are all about events n on. Click, on. Mouse. Over, on. Mouse. Move… w Events can also be based upon time or interactions with the network, operating system, other applications, etc.
Agenda w w Internet Technologies Programming Languages and Paradigms Programming the Web. NET Overview
Programming the Web Client-Side Code w What is client-side code? n Software that is downloaded from Web server to browser and then executes on the client w Why client-side code? n n n Better scalability: less work done on server Better performance/user experience Create UI constructs not inherent in HTML l l n n Drop-down and pull-out menus Tabbed dialogs Cool effects, e. g. animation Data validation
Programming the Web Client-Side Technologies w DHTML/Java. Script w COM n n n w w Active. X controls COM components Remote Data Services (RDS) Java Plug-ins Helpers Remote Scripting
Programming the Web Dynamic HTML (DHTML) w Script that is embedded within an HTML page w Usually written in Java. Script (ECMAScript, JScript) for portability n Internet Explorer also supports VBScript and other scripting languages w Each HTML element becomes an object that has associated events (e. g. on. Click) w Script provides code to respond to browser events
Programming the Web DHTML w The DHTML Document Object Model (DOM) window event navigator history document location screen frames all location children forms selection body links radio button text password file checkbox submit reset textarea select option
Programming the Web Active. X w Based on COM w Native only to Internet Explorer n Supported in Netscape with a plug-in w Good when you know your users (e. g. intranet) or can specify which browser to use w Small, efficient code
Programming the Web Java Applets w Based on Java bytecode w Held great promise as a portable, pain-free way to download client-side code: n “Write once, run anywhere” w Fairly safe: code runs in a “sandbox” w Compatibility and performance issues have prevented common usage
Programming the Web Server-Side Code w What is server-side code? n n Software that runs on the server, not the client Receives input from l l n n 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 w Why server-side code? n Accessibility l n Manageability l l n Does not require distribution of application code Easy to change code Security l l n You can reach the Internet from any browser, any device, any time, anywhere Source code is not exposed Once user is authenticated, can only allow certain actions Scalability l Web-based 3 -tier architecture can scale out
Programming the Web Server-Side Technologies w w w w 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) w Technology to easily create server-side applications w ASP pages are written in a scripting language, usually VBScript or JScript w An ASP page contains a sequence of static HTML interspersed with server-side code w 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 w w Internet Technologies Programming Languages and Paradigms Programming the Web. NET Overview
. NET Overview w w w w Introduction to. NET Web Services The. NET Framework Common Language Runtime Windows Forms Web Forms ADO. NET Languages
Introduction to. NET What is. NET? w A vision of how information technology will evolve w A platform that supports the vision w A business model of software as a service
Introduction to. NET What is. NET? w A vision n n 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? w A platform n n n The. NET Framework Visual Studio. NET Enterprise Servers l n Database, Messaging, Integration, Commerce, Proxy, Security, Mobility, Orchestration, Content Management . NET Building Block Services l l n } The focus of this course Passport. NET My Services (“Hailstorm”) Goal: make it incredibly easy to build powerful Web applications and Web services
Introduction to. NET What is. NET? w A business model n n n Software as a service Subscription-based services Application hosting, e. g. b. Central
Introduction to. NET The. NET Platform Clients Applications Web Form Protocols: HTTP, HTML, XML, SOAP, UDDI Your Internal Web Service . NET Framework Windows . NET Foundation Web Services Third-Party Web Services Tools: Visual Studio. NET, Notepad . NET Enterprise Servers
Web Services w A programmable application component accessible via standard Web protocols w The center of the. NET architecture w Exposes functionality over the Web w Built on existing and emerging standards n HTTP, XML, SOAP, UDDI, WSDL, …
Web Services Evolution of the Web HTML, XML HTML, XML Generation 1 Static HTML Generation 2 Web Applications Generation 3 Web Services
The. NET Framework What Is the. NET Framework? w A set of technologies for developing and using components to create: n n n Web Forms Web Services Windows Applications w Supports the software lifecycle n n Development Debugging Deployment Maintenance
The. NET Framework and Visual Studio. NET VB C++ C# JScript … ASP. NET: Web Services and Web Forms Windows Forms ADO. NET: Data and XML. NET Framework Base Classes Common Language Runtime Visual Studio. NET Common Language Specification
The. NET Framework Classes System. Web Services Description Discovery Protocols UI Html. Controls Caching Configuration Security Session. State System. Windows. Forms Form Button Message. Box List. Control Web. Controls System. Drawing 2 D Imaging System. Data OLEDB Design SQLTypes Printing Text System. Xml XSLT XPath Serialization System Collections Configuration Diagnostics Globalization IO Net Reflection Resources Security Service. Process Text Threading Runtime Interop. Services Remoting Serialization
Common Language Runtime Goals w Development services n n Deep cross-language interoperability Increased productivity w Deployment services n n Simple, reliable deployment Fewer versioning problems – NO MORE ‘DLL HELL’ w Run-time services n n n Performance Scalability Availability § Reliability § Security § Safety
Common Language Runtime Compilation Source Code Assembly Compiler C++, C#, VB or any. NET language csc. exe or vbc. exe DLL or EXE
Common Language Runtime Assemblies w Assembly n n Logical unit of deployment Contains Manifest, Metadata, MSIL and resources w Manifest n Metadata about the components in an assembly (version, types, dependencies, etc. ) w Type Metadata n Completely describes all types defined in an assembly: properties, methods, arguments, return values, attributes, base classes, …
Common Language Runtime Assemblies w Microsoft Intermediate Language (MSIL, IL) n n All languages compile to IL (managed code) IL is always compiled to native code before being executed w Resources n E. g. . bmp, . jpg
Common Language Runtime Execution Model Source code MSIL Ngen Native code VB C# C++ Compiler Assembly Common Language Runtime JIT Compiler Managed Code CLR Services Managed CLR Code Managed Code Operating System Services Unmanaged Code
Common Language Runtime Services w Code management w Conversion of MSIL to native code w Loading and execution of managed code w Creation and management of metadata w Verification of type safety w Insertion and execution of security checks w Memory management and isolation w Handling exceptions across languages w Interoperation between. NET Framework objects and COM objects and Win 32 DLLs w Automation of object layout for late binding w Developer services (profiling, debugging, etc. )
Common Language Runtime Multiple Language Support w Common Type System (CTS) n A superset of the data types used by most modern programming languages w Common Language Specification (CLS) n A subset of CTS that allows code written in different languages to interoperate w What languages? n n Microsoft: C++, Visual Basic, C#, JScript Third-Party: Cobol, Eiffel, Smalltalk, Scheme, Oberon, Haskell, Java, Python, Perl, …
Common Language Runtime Applications w An application consists of one or more assemblies w How does one assembly bind to another? n Based upon metadata and policy l l Local (preferred) Assembly Global Cache w Multiple versions of an assembly may exist on the same machine n n Easier software deployment, updates and removal Multiple versions of an assembly can even be used by the same application
Common Language Runtime Security w w Evidence-based security (authentication) Based on user identity and code identity Configurable policies Imperative and declarative interfaces
Windows Forms w Framework for building rich clients w Built upon. NET Framework, languages w Rapid Application Development (RAD) w Visual inheritance w Anchoring and docking w Rich set of controls w Extensible controls w Data-aware w Easily hooked into Web Services w Active. X support w Licensing support w Printing support w Advanced graphics
Web Forms w Built with ASP. NET n n Logical evolution of ASP Similar development model: edit the page and go w Requires less code w New programming model n n n 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 w Allows separation of UI and business logic w Uses. NET languages n Not just scripting w Easy to use components w XCOPY/FTP deployment w Simple configuration (XML-based)
Web Forms w w Caching (pages, fragments, custom) Scalable session state management Tracing support ASP. NET is extensible n No ISAPI / ASP dichotomy w Automatic process rollover w Forms-based authentication
ADO. NET w Similar to ADO, but better factored w Language-neutral data access w Supports two styles of data access n n Disconnected Forward-only, read-only access w Supports data binding w Data. Set: a collection of tables w Can view and process data relationally (tables) or hierarchically (XML)
Languages C# w New language created for. NET w Safe, productive evolution of C++ w Key concepts: n n Component-oriented Everything is an object Robust and durable code Preserving your investment w Submitted to ECMA for standardization w Uses. NET Framework classes
Languages Visual Basic. NET w Modernizes and simplifies Visual Basic n n n Inheritance Threading Exception handling w Support for late binding w Uses. NET Framework classes
Conclusion w w Internet Technologies Programming Languages and Paradigms Programming the Web. NET Overview
More Resources w HTTP n n http: //msdn. microsoft. com/library/periodic/period 96/protocol. htm HTTP Essentials, Stephen Thomas, 2001, Wiley, ISBN 0471 -39823 -3 w Cookies n http: //msdn. microsoft. com/library/default. asp? URL=/library/partb ook/instantj/cookies. htm w MIME n n http: //www. ufaq. org/navcom/mime_tutorial. html http: //www. irvine. com/~mime/ w Networks n http: //msdn. microsoft. com/library/periodic/period 99/ntp 99 b 3. htm
More Resources w XML n n n http: //msdn. microsoft. com/xml/default. asp http: //www. w 3. org/XML/ Essential XML, Don Box, Aaron Skonnard, John Lam, Addison Wesley, 2000, ISBN 0 -201 -70914 -7 w. NET n n http: //www. microsoft. com/net/ http: //msdn. microsoft. com/net/ http: //www. gotdotnet. com msnews. microsoft. com news server l microsoft. public. dotnet. general newsgroup
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