1 Web and DB - INT Evry Web and databases Bruno DEFUDE Computer Science Dept

1Web and DB - INT Evry

Web and databases

Bruno DEFUDEComputer Science Dept


WWW – Web advantages

Universal client Easy to use Open standards Good integration with other Internet services and

protocols Extensible Low software and network costs Corporate network (Intranet), inter-companies

network (extranet), WAN


Why coupling web and DB?

Web is a kind of DB but» Without schema» Without query language» Without transactions, recovery, …» Without powerfull authorisation mechanism

DBs store huge amount of data which are interesting to publish on the web


Simple coupling

Transform DBs into sets of static web pages» Simple» Redundency, problem of consistency» Disadvantages of web

Need to generate dynamic web pages constructed with DB content


First solution: CGI scripts

Browser (client)

HTTPserver

DBMS

url

Html result

CGI

querystring

SQLHTML


Pros and Cons of CGI

Simple and portable Lots of code to write (one CGI per

query!): can be improved with generic solutions

Not very efficient


WWW – CGI problem

Client 1

Client 2

Client 3

C

G

I

Server Process

Process 1

Process 1

Process 1HTTP Server

CGI Scripts


WWW – the API Solution

Client 1

Client 2

Client 3

Server Process

HTTP Server

API

Set of functions

Thread 1

Thread 2

Thread 3

CGI scripts are functions of a DLL, Processed As threads within the multi-threaded HTTP server


FastCGI Persistent CGI script CGI (daemon like) A fastcgi script is splitted into 3 parts:

» init : process one time» body : process at each request» ending : process one time

Init part must include costly part of the CGI code (connection to a DBMS, …)

Well adapted to DBMS access, but is persistent (can not handle numerous different connections)


WWW – Web limitations

performances» Internet network => increase bandwith» CGI scripts => FastCGI, server-side scripts

security» HTTP => S-HTTP secure» TCP/IP level => SSL protocol


WWW – Web Limitations (2)

Transaction management» not possible with HTTP 1.0

– no session mode– One can use "cookies"

» Possible with HTTP 1.1– Allows persistent connexion (TCP level)

User interface» HTML is not very powerfull to construct sophisticated

UI» Java is more powerfull


WWW – Web evolutions

At the beginning» access to informations

– Distributed on the network– Represented by hypermedia documents

today» Software construction and processing

– client/server, heterogeneous– Inside the same organization (Intranet)


Coupling Web and DBMS

Gateways Principles Java approach (applets, servlets, JSP) Server-side scripting (PHP)


Gateways Principles

Single-request gateways Multiple-request gateways

(transactional)


Functionalities

(1) translate HTTP request (mapping environment variables to SQL statements)

(2) process SQL queries on the DBMS (3) encode SQL results as HTML pages


Process SQL queries

Program written using a DBMS API» DBMS-dependent approach (embedded

SQL)» DBMS-independent approach (ODBC,

JDBC or DBI for Perl) Programming languages used

» classical : C, C++, Ada, … if embedded SQL

» Scripting language : Perl (with DBI)


HTML encoding Generic solution (can be automated):

» select : HTML table» other query : string

Specific solution: a specific program for each query

– Within the gateway (one gateway / query !)– Within the DBMS (one stored procedure / query)

Intermediate solution:» encoding can be parametrized (update form,

hypertext navigation within the DB ,…)


DB access (simple html)

Browser (client)

HTTPserver

DBMS

url

Html result

CGI

Gateway

querystring

SQL data

HTML


Simple HTML example

<html><body><form name="f1" action="http://mica/multi2.cgi" method="get"><input type="hidden" name="uid" value="citcom/citcom@MICA"><input type="hidden" name="sqlstatement"

value="select * from students where sname=">Give a name : <input name="sname" value=""><p><input type="submit" value="lancer"></form></body></html>


DB access (client-side script)

Browser (client)

HTTPserver

DBMS

url

Html result

gatewayquerystring

SQL data

HTML


HTML with Javascript example

<html><body><form name="f1" action="http://mica/multi2.cgi" method="get"><input type="hidden" name="uid" value="citcom/citcom@MICA"><input type="hidden" name="sqlstatement"

value="select * from students where sname=">Give a name : <input name="sname" value=""><p><input type="button" value="go"

onClick="f1.sqlstatement.value+=f1.sname.value; f1.submit();">

</form></body></html>


DB access (without http)

Browser (client)+ java, TCL program (applet, tclet …)

DBMS

Specificprotocol

Specific protocol: JDBC, IIOP (CORBA)


Functionalities

(1) (2) (3)

Simple HTML

Client-sidescript

without http

SpecificCGI DBMS

DBMS

DBMS

gateway orDBMS

gateway orDBMS

client

client


Variations

DBMS-dependent or independent (native or ODBC)

Supported query language (SQL or subset, static vs dynamic)

HTML encoding (generic or specific) efficiency


Efficiency

CGI vs NSAPI, ISAPI (but proprietary solutions)

Decrease process number (if large number of clients) : multithreaded gateway


Transactions

transaction = DB program (read and write sequence)

ACID properties– A : Atomicity– C : Consistency– I : Isolation– D : Durability


Examples of transactional services

on-line ordering (music, books, planes, …)

bank insurance e-business!!!!


Transactions and Web

Transaction = sequence of URL invocations (management context by the web?)

Transaction = ACID properties (ensured by the DBMS)

HTTP = no session support– Client-side management context (cookies)– Simulation of HTTP sessions (transactional web)– Use server-side scripting languages (PHP, ASP, JSP, ...)


Transactions and cookies

Browser (client) http server cgi

DBMS

1 11’ c11’ c1

2 c1 2 c12’ c1, c2 2’ c1, c2

3 fin c1, c2 3 fin c1, c2

4 sql(c1, c2)

5’ del(c1, c2) 5’ del(c1, c2)4’ ok1 : first access

1’ : c1 cookie is generated2 : other access with c1 cookie transport2’ : c1, c2 cookies are generated3 : end of transaction with c1, c2 transport4 : transaction is constructed and processed on the DBMS5’ : cookies deletion


Transaction and cookies (2)

Context is managed on client-side (cookies)

advantages:– Easy to code– DB access is done one time at the end of the

session (DB resources are not blocked)– If no explicit user termination, nothing to do (at

DB level)


Transaction and cookies (3)

Cons– Not really transactional– Limited functionality– Lots of cgi scripts to code

Cookies problems– global to a user (no distinction between two

windows)– global to a url (does not allow two different

transactions on the same site at the same site)


transactional gateway

browser (Client) http Server cgi daemon gateway DBMS


transactional gateway principles

Context is managed by a daemon on server-side

Need of a transaction id stored on client-side (cookie or rewritten URL) and on server-side (in an array of the daemon)

A gateway does not process a single query but a complete transaction (a sequence of queries)


transactional gateway operations (1)

1 : transaction beginning request (implicite or explicite)

– An id is allocated by the daemon, transactions array is updated, a gateway is launched, an id is send back to the client (cookie or rewritten URL)

2 : DB operation request – The request is routed by the daemon on the

right gateway using the transaction id and the transactions array


transactional gateway operations(2)

3 : transaction ending request– implicit : error, timeout

– explicit : idem 2 + update of transactions array, id is deleted on client-side and the gateway is stopped


transactional gateway Resume

Pros– really transactional– generic solution

Cons– complex architecture – DB resources are blocked until the end of the

transaction– Need to detect a user « abort » (timeout)


Scripting language (server-side)

Offer a programming language integrated to the web (ability to have calls from a web page, associated to a HTTP server)

run-time of the language offers session support (and consequently of transactions)

PHP, servlet - JSP, ASP, XSP (Cocoon) see Java and PHP for more details


Java and Web

JVM concept is well adapted for Web Java language is widely used JDBC (standard API for DBMSs) Applets servlets Java Server Pages


Java - Java and Web

language for W3 client» applet = small compiled Java application

– Loaded from a W3 server

– Running is secured by the client JVM

language for W3 server » servlet = compiled Java application

– Stored on server-side

– Run by server-side JVM


Servlets

Servlet 2.2 (http://java.sun.com/servlet) Tomcat from Apache is the reference

implementation Same as CGI for Java CGI extensions (session, buffer

management, redirection/chaining)


Servlet Architecture

WebbrowserClient Servlet container

servlet2servlet1

HTTPServer

Container manages servlets (activation, desactivation)


Servlet object Model

request Object servlet1 Response Object

session Object

getParametergetAttributegetHeadersgetCookies

setBufferSizesetHeadersetRedirect

getAttribute


JSP JSP 1.2 (http://java.sun.com/jsp) Tomcat from Apache is the reference

implementation Scripts included into HTML pages Same as ASP, PHP but for Java compiled into servlets portability of Java Server-side scripting with extensibility using tag

libraries


Example of JSP page<html><%@ page language=« java » import=« java.util.* » %><h1>Welcome</h1><p>Date: <p><jsp:usebean id=« clock » class=« jspCalendar »/><ul><li>Day : <%= clock.getDayOfMonth() %><li>Year : <%= clock.getYear() %></ul><%-- Test for AM or PM --%><%! Int time = Calendar.getInstance().get(Calendar.AM_PM); %><% if (time == Calendar.AM) { %>Good Morning<% } else { %>Good Afternoon<% } %><@ include file=« copyright.html » %></html>


JSP page Components (1)

JSP actions (or tags) : allow to call beans (XML syntax)

directives : processed by JSP engine during page compilation into servlets (include, import, ...)

declarations : as in Java


JSP page Components (2)

expressions : variables or constants integrated into the HTML result page

scriplets : blocks of Java code integrated into a JSP page

comments


Personalized Tags

One can add his/her own tags to simplify JSP page writing

tags libraries mechanism to define new tags is

complex


Example use of tag libraries

<html><%@ taglib uri=« http://acme.com/taglibs/simpleDB.tld »prefix=« x » %><x:queryBlock connData=« defude/bruno@MICA »> <x:queryStatement>select number, sname from students

</x:queryStatement> The first 10 students are: <table> <tr><th>Number</th><th>Name</th> <x:queryCreateRows from =« 1 » to=« 10 »>

<td><x:queryDisplay field=« number »/></td><td><x:queryDisplay field=« sname »/></td>

</x:queryCreateRows> </table></x:queryBlock></html>


Example (cont)

Definition of a queryBlock tag composed itself by other tags (queryStatement, queryCreateRows)

Allow to mask JDBC code to the page developer

a tag is defined by a descriptor (XML document) + a Java class for implementation


XML and Web

XML offers a clear splitting between logical structure and presentation

Allow to develop software producing different format outputs of the same XML source (HTML vs PDF, WML vs HTML,...)


Publishing Environment for XML

Software environment allowing to produce different output formats from the same XML source

Cocoon from XML-Apache Often based on Java implementation

(Servlet, JSP)


Cocoon

Web browseror PDA Client

Doc.XML

XSLT Interpreter

FOP InterpreterPDF Doc.

HTML Doc.

WML Doc.

Cocoon

1 2

4

4

56

Apache+ Tomcat

3


Conclusion

Numerous software products and several solutions

choice depends on the objective:» Query web site: simple gateways of server-side

scripting language PHP, ASP» Different web sites produced from the same

source: XML» Corporate portals: JSP or Cocoon

Documents

1 Web and DB - INT Evry Web and databases Bruno DEFUDE Computer Science Dept