Chapter 11 Web-based Information Systems

Transcription

1 Prof. Dr.-Ig. Stefa Deßloch AG Heterogee Iformatiossysteme Geb. 36, Raum 329 Tel. 0631/ Chapter 11 Web-based Iformatio Systems

2 TP Applicatio Architecture Frot-ed program iteracts with (possibly wide rage of) display devices gathers ad validates iput, displays output costructs ad forward request (e.g., as a RPC or asychroous message) è provides device-idepedece for server Request cotroller guides the request executio determies required steps, the executes them by ivokig trasactio servers usually rus as part of a ACID trasactio Trasactio server process that rus applicatio programs doig the actual work of the request almost always rus withi the scope of a ACID trasactio typically iteracts with a DBMS simple applicatios ca be composed ito more complex oes (usig local proc. call, TRPC, asych. messagig, ) makes differece to req. cotroller fuzzy Trasactio Server Database System DB cliet Frot-ed Program Request Cotroller Trasactio Server Database System DB... frot-ed server Trasactio Server DBMS Prof.Dr.-Ig. Stefa Deßloch 2 Middleware for Heterogeeous ad Distributed Iformatio Systems

3 Frot-ed Program Fuctios Gather iput ad display output (user iteractio) form ad meu cocepts user selects a meu item to idetify the type of trasactio to be executed frot-ed program display a (series of) form(s) for gatherig iput data iput data is validated by the frot-ed program goal: avoid callig the TP-server with icorrect iput based o geeral data type/format, possibly usig cached data values presetatio techologies support form ad meu cocepts defie meus ad how to avigate betwee them defie fields ad scree layout of forms idetify data validatio routies to be called for each field Costruct requests ad iterpret replies request ca take the form of a RPC or (a)sychroous message typically icludes user idetifier device idetifier (e.g., etwork address) request type iput parameters Prof.Dr.-Ig. Stefa Deßloch 3 Middleware for Heterogeeous ad Distributed Iformatio Systems

4 Web-based IS Iitial purpose of the WWW: sharig iformatio o the iteret techologies HTML documets HTTP protocol web browser as cliet for iteret iformatio access For Iformatio Systems: coectig remote cliets with applicatios across the iteret/itraet "web-eabled" applicatios exted applicatio reach to the cosumer leverage advatages of web techologies web browser as a uiversal applicatio cliet/frot-ed program "thi cliet" o applicatio-specific cliet code has to be istalled requiremets cotet is comig from dyamic sources (IS, DBS) request to access a resource has to result i applicatio ivocatio sessio state: trackig repeated iteractios of the same cliet with a web server Prof.Dr.-Ig. Stefa Deßloch 4 Middleware for Heterogeeous ad Distributed Iformatio Systems

5 Forms Techologies ad Tools Desig time Ru time Thi Cliet HTML/XML Forms Editor DreamWeaver Expressio Web HTML Forms XHTML Dyamic HTML AJAX Web Server Ed-user device Thick Cliet Visual Studio Eclipse-based IDE NetBeas Visual Basic, C# Java Eclipse RCP Request Cotroller Prof.Dr.-Ig. Stefa Deßloch 5 Middleware for Heterogeeous ad Distributed Iformatio Systems

6 Architecture for Web-IS Presetatio layer may be realized i separate tiers cliet web browser cliet-side presetatio usig browser, cliet compoets (optioal) server-side presetatio doe by web server, dyamic HTML geeratio (HTML filter) Presetatio compoets iteract with applicatio logic compoets maaged by appl. server, or ru withi web server eviromet Access to RM layer "ecapsulated" i appl. logic compoet may also be performed directly withi presetatio logic compoet special case, if there is o applicatio logic (oly data access logic) presetatio layer web server HTML filter applicatio (or web) server applicatio logic resource maagemet layer iformatio system Prof.Dr.-Ig. Stefa Deßloch 6 Middleware for Heterogeeous ad Distributed Iformatio Systems

7 Overview Web Browser (Cliet) 1 persistet (applet) program cache Proxy Server HTML: HyperText Markup Laguage CGI: Commo Gateway Iterface HTTP: HyperText Trasfer Protocol JSP: Java Server Page 6 2 Commuicatio Server JVM Web Server Servlet, JSP SSI, Server extesio 3 CGI programs HTML images applets scripts 4 Applicatio Server + DB-Server Prof.Dr.-Ig. Stefa Deßloch 7 Middleware for Heterogeeous ad Distributed Iformatio Systems

8 Server Compoets WWW-Server core compoet provides static HTML pages, icl. embedded images, etc. (u, v) provides Java applets, which may access a DB either directly (y) or via a commuicatio server (z, {) ivokes server-side extesios (w) ivokes CGI programs (w) ivokes Java servlets, Java Server Pages (JSPs) ( ) delivers results of TP iteractios (CGI programs x, Java servlets }) as dyamically geerated HTML to web browser Prof.Dr.-Ig. Stefa Deßloch 8 Middleware for Heterogeeous ad Distributed Iformatio Systems

9 Server Compoets (2) DB-Server maages applicatio data may maage static HTML pages (or fragmets) Applicatio-Server maages ad executes request cotrollers ad trasactio servers Proxy-Server caches results (HTML documets, images) of a HTTP request to improve respose time for static iformatio requests dyamically geerated or specially marked documets are ot cached Commuicatio-Server ca be used to support DB-Server coectivity for Java applets (z, {) Prof.Dr.-Ig. Stefa Deßloch 9 Middleware for Heterogeeous ad Distributed Iformatio Systems

10 Core Techologies Cliet-side Java Applets, Javascript Server-side Commo Gateway Iterface (CGI) programs Web Server API Java Servlets Server-side Icludes (SSI) Java Server Pages (JSP) Prof.Dr.-Ig. Stefa Deßloch 10 Middleware for Heterogeeous ad Distributed Iformatio Systems

11 Cliet-Side Approaches Goal: applicatio-specific, dyamic cliets itegrated ito the web browser Capabilities applicatio modules ca be dowloaded (at ru-time) to the cliet ad executed do't eed to be pre-istalled prior to ivocatio module ca access applicatio server or DB server may result i performace beefits module ca maage state across multiple iteractios Prof.Dr.-Ig. Stefa Deßloch 11 Middleware for Heterogeeous ad Distributed Iformatio Systems

12 Java Applets Applicatio compoet embedded i HTML page (similar to images), stored o the web server Dyamically trasferred to the cliet to be executed i a Java-eabled web browser (u, v) requires JVM itegrated ito web browser or loaded by Java plug-i Applets ca use full Java laguage support JAR files (Java ARchive) ca be used to package all class files eeded by a applet for dowload over the etwork Geeral security restrictios (utrusted applets) o access to local resources etwork commuicatio restricted to server of origi Siged Applets Security cocept for applets (sice JDK 1.1) JAR file cotais digitally siged applet files ad digital certificate guaratee that applet has ot bee modified after siged by providig party cliet may trust applets, grat permissios based o certificates Ca be stored persistetly o the cliet side Prof.Dr.-Ig. Stefa Deßloch 12 Middleware for Heterogeeous ad Distributed Iformatio Systems

13 Applet-based DB Access Usig JDBC/SQLJ Type 3 driver improved security commuicatio server for load balacig works with usiged applets commuicatio overhead (loger respose times) Type 4 driver direct commuicatio requires either siged applets or idetical DB-server ad web server locatio Additioal alteratives ad APIs ODMG Java-Bidig for access OODBMS defies laguage bidig for ODL (Object Defiitio Laguage) to Java API for executig OQL(Object Query Laguage) statemets ad processig of results other Java-DB APIs proprietary, DBMS-vedor-specific Java-APIs applet implemetatios ot portable Prof.Dr.-Ig. Stefa Deßloch 13 Middleware for Heterogeeous ad Distributed Iformatio Systems

14 Iteractio with Applicatio Compoets CORBA sice CORBA 2.2: Java Laguage Bidig, supported by umerous ORBs with Java support Java-IDL CORBA-compliat ORB, ca commuicate with server objects ad server-side ORBs usig IIOP (Iteret Iter Orb Protocol) available i all Java-eabled browsers as part of JDK 1.2 avoids dowloadig CORBA rutime Java Remote Method Ivocatio (RMI) iteroperability with CORBA/EJB RMI over IIOP Prof.Dr.-Ig. Stefa Deßloch 14 Middleware for Heterogeeous ad Distributed Iformatio Systems

15 Applet-based Architecture for Web-IS Web Browser (Cliet) RMI persistet (applet) program cache HTTP Web Server HTML images applets IIOP Applic. Server Type 3 Commuicatio Server applicatio objects Type 4 DB-Server Prof.Dr.-Ig. Stefa Deßloch 15 Middleware for Heterogeeous ad Distributed Iformatio Systems

16 Evaluatio: Advatages Ehaced UI-support HTML oly supports presetatio of alpha-umeric data, potetially i tabular form applets ca leverage Java to process data ad visualize complex data structures (e.g., geometry/cad data) complete UI has to be implemeted i Java trasiet storage of state withi applet, across multiple user iteractios Coectivity, trasactios applet may coect directly to DB-Server (y) Coectio-Server (z, {) Applicatio-Server applet state ca preserve DB-coectios across iteractios log, multi-step trasactios distributed trasactios Prof.Dr.-Ig. Stefa Deßloch 16 Middleware for Heterogeeous ad Distributed Iformatio Systems

17 Evaluatio: Disadvatages Loadig time higher iitial loadig time due to dowloadig applet (applicatio logic, UI) from web server solutio: persistet program cache i combiatio with siged applets applets ca be held persistetly at cliet alterative: use of Java iterfaces, delayig dowload of implemetatio Java security usiged applet ca oly coect back to server of origi web, DB/coectio server have to reside o the same machie (-> bottleeck) this restrictio ca be avoided by usig siged applets ad appropriate cliet security policies No adequate support for combied cliet/server-side trasactios passig trasactio cotext to server-side web compoets ot supported by HTTP Requires eablig/allowig coectio to DB server systems from web cliets may be suitable for the itraet questioable for iteret scearios (security, firewalls, ) Prof.Dr.-Ig. Stefa Deßloch 17 Middleware for Heterogeeous ad Distributed Iformatio Systems

18 Cliet-Side Processig JavaScript object-orieted scriptig laguage (sytax similar to Java) ca be embedded i or refereced from withi a web page script ca iteract with the Documet Object Model (DOM) of the web page ca maipulate the page/html ca react to user evets Web browser eeds to support the JavaScript laguage iterprets the script elemets Mai use implemet user iterface logic of a web page validate web forms make web pages more iteractive, dyamic ad resposive Prof.Dr.-Ig. Stefa Deßloch 18 Middleware for Heterogeeous ad Distributed Iformatio Systems

19 Ajax Origially a shorthad for Asychroous JavaScript ad XML Idicates a set of techologies used for web applicatios presetatio based o XHTML, CSS dyamic display ad iteractio usig Documet Object Model data iterchage ad maipulatio usig XML, XSLT asychroous data retrieval usig XMLHttpRequest JavaScript (bidig everythig together) Ajax variatios use of aother scriptig laguage (e.g., VBScript) data iterchage based o JavaScript Object Notatio (JSON) or others Mai beefits avoids reloadig complete pages, oly iteracts with server for subset of the cotet or avoids iteractios altogether user perceives web applicatio as faster, due to asychroous loadig of data state preserved iside JavaScript variables across multiple iteractios mai cotaier page is ot reloaded Prof.Dr.-Ig. Stefa Deßloch 19 Middleware for Heterogeeous ad Distributed Iformatio Systems

20 Server-side Approaches Idea web server ca execute program compoet based o cliet request may perform data access operatios ca iteract with other busiess logic compoets (e.g., EJBs, JavaBeas, ) program dyamically geerates required resource (e.g., HTML documet) Approaches CGI programs Server API Java Servlets Server-Side-Icludes Java Server Pages (JSPs) Prof.Dr.-Ig. Stefa Deßloch 20 Middleware for Heterogeeous ad Distributed Iformatio Systems

21 Commo Gateway Iterface (CGI) Programs Dyamic geeratio of HTML documets based o CGI ad HTML forms Web server starts CGI program i a separate process CGI program ispects eviromet variables set by web server Web server commuicates parameters provided i HTML forms to CGI program i a well-defied maer (w) CGI program ca access DB-server usig DB cliet APIs (x) CGI program geerates HTML documet ad returs it to the web server as the result of the program executio Web server passes the resultig HTML back to the cliet (web browser) Prof.Dr.-Ig. Stefa Deßloch 21 Middleware for Heterogeeous ad Distributed Iformatio Systems

22 Server API (for Server Extesios) Web server vedors provide proprietary APIs to avoid creatio of separate process for CGI program Examples: NSAPI (Netscape Server API), Netscape ISAPI (Iteret Server API), Microsoft Meas to exted web server capabilities with additioal fuctios (Server Applicatio Fuctio, SAF) that previously had to be realized usig CGI SAFs are provided as dyamic program libraries, liked to web server at startup time Web server ca distiguish regular HTML documet access from SAF ivocatio based o URL ad cofiguratio data (w) Performace advatage over CGI avoids creatio of separate process DB-coectio ca be kept ope Prof.Dr.-Ig. Stefa Deßloch 22 Middleware for Heterogeeous ad Distributed Iformatio Systems

23 Java Servlets SUNs respose to server extesios by Netscape, Microsoft for Java-based web server Icluded i JDK 1.2, supported by may web server implemetatios Supports platform-idepedet ad vedor-idepedet extesibility of web servers Primary approach for realizig web applicatios i J2EE web applicatio server itegrates support for ad iteractio of web compoets (e.g., servlets) ad applicatio compoets (EJBs) Requires itegratio of JVM i web server ( ) or cooperatio of web server with associated JVM process Follows the same model as C-based server APIs Additioal advatage: dyamic bidig of Java class loader -> uiterrupted web server executio Prof.Dr.-Ig. Stefa Deßloch 23 Middleware for Heterogeeous ad Distributed Iformatio Systems

24 Server-Side Icludes (SSI) Directives icluded i HTML documet as HTML extesios Dyamically evaluated by web server whe documet is requested by cliet Ca be used to iclude curret date, time or other status iformatio ito the web page ivoke applicatios ad OS commads access DB-server Web-server-specific extesios Prof.Dr.-Ig. Stefa Deßloch 24 Middleware for Heterogeeous ad Distributed Iformatio Systems

25 Java Server Pages (JSPs) Server-side scriptig HTMP page templates cotai programmig istructios that are to be executed by a server program (web server scriptig egie) to build the dyamic cotet (plai HTML) of the web page popular approaches: PHP, Java Server Pages, JSPs are based o SSI, servlets JSPs are traslated (oce) ito servlets for executio Mixes static HTML with embedded JSP costructs for presetig dyamic cotet scriptig elemets Java code to be icluded i servlet directives cotrols overall structure of servlet actios allow for use of existig compoets Stadard/custom tag libraries, ivocatio of JavaBeas compoets separatio of programmig ad page desig/developmet cocers ad roles Prof.Dr.-Ig. Stefa Deßloch 25 Middleware for Heterogeeous ad Distributed Iformatio Systems

26 Sessio Support Stateful iteractios may deped o the outcome of previous steps Server-side approaches are based o HTTP HTTP is a stateless protocol does ot provide direct support for storig iformatio that persists across HTTP iteractios problems DB-cliets realized with CGI, Server-APIs are oly "active" for the duratio of a sigle iteractio o trasactios across multiple requests ew coectio has to be obtaied for every HTTP request resultig i DB-access egative impact o respose times Sessio support is required sessio trackig: associate all requests of a sigle user with a sessio sessio state: state iformatio has to be stored ad maaged by the server/applicatio Prof.Dr.-Ig. Stefa Deßloch 26 Middleware for Heterogeeous ad Distributed Iformatio Systems

27 Sessio Trackig Sessio may cosist of multiple steps (e.g., maagig a shoppig cart) cliet state (cotext) eeds to be stored/maaged ad made available to server compoets Sessio-ID ad User-ID (to avoid repeated autheticatio) required icluded as tokes or coversatio idetifiers i cliet/server iteractios Commo techiques Form variables (hidde form fields) URL ecodig HTTP-Cookies HTTP-Autheticatio Use of the techiques explicitly by the programmer implicitly through higher-level programmig iterfaces Example: HttpSessio-Iterface for Servlets Prof.Dr.-Ig. Stefa Deßloch 27 Middleware for Heterogeeous ad Distributed Iformatio Systems

28 Form Variables Sessio-ID is icluded i HTML forms as a hidde variable by server <INPUT TYPE=HIDDEN NAME=SID VALUE=4711> Value is trasmitted back to web server together with form iput, ca be used to establish associatio with sessio cotext Ca be used with all cliet cofiguratios, supported for every browser ad browser cofiguratio Forces developer to use dyamic HTML documets with form submissios for all iteractios, because Sessio-ID eeds to be iserted ito all HTML documets potetially causig subsequet stateful iteractios respose times suffer complicates applicatio developmet Prof.Dr.-Ig. Stefa Deßloch 28 Middleware for Heterogeeous ad Distributed Iformatio Systems

29 URL Ecodig Ecodig sessio/user-id i the URL as a path parameter ( /ews/overview;id=4711 ) pages are dyamic, each URL o the page is persoalized by the server cliet request ow re-trasmits the id web server/cgi program eeds to extract the ID from the URL ad perform the appropriate actio Supported i all cofiguratios ad browsers Agai, all pages eed to be dyamic! Overall, realizatio is complex, persoalized URL is ot user-friedly Prof.Dr.-Ig. Stefa Deßloch 29 Middleware for Heterogeeous ad Distributed Iformatio Systems

30 HTTP-Cookies Idepedet of web documets Cookies are pieces of text that ca be trasmitted by the server, together with the meta data of the HTML, stored temporarily at the cliet Automatically icluded i web server iteractio by the browser (util cookie is ivalidated) Example: the strig Set-Cookie: ID= 4711 ; Versio= 1 ; Path= /catalog ; Max-Age= 1800 is trasmitted to browser, together with the HTML documet every request to the web server that icludes the subdirectory catalog will iclude Cookie: ID=4711 cookie is valid oly for 1800 secods Disadvatage: cookies may be disabled by the browser/cliet Prof.Dr.-Ig. Stefa Deßloch 30 Middleware for Heterogeeous ad Distributed Iformatio Systems

31 HTTP-Autheticatio REMOTE_USER eviromet variable ca be used by CGI program to correlate requests Advatage: automatically supported by browser ad web server Disadvatage: user registratio ad autheticatio before every sessio Prof.Dr.-Ig. Stefa Deßloch 31 Middleware for Heterogeeous ad Distributed Iformatio Systems

32 Compariso Form variable URL ecodig HTTP-Cookie HTTP-Autheticatio Pros Idepedet of browser type ad user prefereces. Idepedet of browser type ad user prefereces. Automatic browser support; Idepedet of HTML documet. Automatic browser ad web server support; Idepedet of HTML documet. Cos Has to be icluded i every HTML page to be displayed by the browser; Dyamic HTML complicates applicatio developmet. Dyamic pages; [Complex traslatio of HTTP requests.] User cofiguratio eeds to permit use of cookies. Requires user registratio ad autheticatio. APIs ca help reduce complexity (e.g., servlet APIs) Problem with all techiques: choosig timeout values for server-side termiatio of sessio due to iactivity of user importat for releasig server resources suitable values for timeout are applicatio-depedet Prof.Dr.-Ig. Stefa Deßloch 32 Middleware for Heterogeeous ad Distributed Iformatio Systems

33 Summary Web-based applicatios become ubiquitous, cocepts for web-based IS are therefore icreasigly importat web browser as a simple, uiform user iterface etworks become more powerful Server-side, HTTP-based approaches suitable for wide rage of applicatios server compoets server-side scriptig Cliet-side, applet-based approaches may be suitable for applicatios with specific UI requiremets data access i itraet eviromets Techiques for maagig sessio state URL ecodig, HTTP-Cookies most commoly used Prof.Dr.-Ig. Stefa Deßloch 33 Middleware for Heterogeeous ad Distributed Iformatio Systems