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Web and databases
Bruno DEFUDE
Computer Science Dept
Web and DB - INT Evry
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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
Web and DB - INT Evry
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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
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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
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First solution: CGI scripts
HTTP
server
CGI
url
query
string
Html result
Browser (client)
SQL
DBMS
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HTML
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
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WWW – CGI problem
Client 1
Client 2
Client 3
Process 1
C
G
I
Server
Process
HTTP Server
Process 1
Process 1
CGI Scripts
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WWW – the API Solution
Client 1
HTTP Server
Server
Process
Client 2
Client 3
API
Thread 1
Set of
functions
Thread 2
Thread 3
CGI scripts are functions of a DLL,
Processed As threads within the multi-threaded
HTTP server
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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)
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WWW – Web limitations
performances
» Internet network => increase bandwith
» CGI scripts => FastCGI, server-side scripts
security
» HTTP => S-HTTP secure
» TCP/IP level => SSL protocol
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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
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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)
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Coupling Web and DBMS
Gateways Principles
Java approach (applets, servlets, JSP)
Server-side scripting (PHP)
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Gateways Principles
Single-request gateways
Multiple-request gateways
(transactional)
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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
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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)
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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 ,…)
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DB access (simple html)
HTTP
server
CGI
url
Html result
Browser (client)
query
string
HTML
SQL
data
Gateway
DBMS
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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>
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DB access (client-side script)
HTTP
server
url
query gateway
string
HTML
SQL
Html result
Browser (client)
data
DBMS
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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>
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DB access (without http)
DBMS
Specific
protocol
Browser (client)
+ java, TCL program (applet, tclet …)
Specific protocol: JDBC, IIOP (CORBA)
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Functionalities
(1)
(2)
(3)
Specific
gateway or
Simple HTML CGI
DBMS DBMS
Client-side
script
without http
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client
DBMS gateway or
DBMS
DBMS client
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Variations
DBMS-dependent or independent
(native or ODBC)
Supported query language (SQL or
subset, static vs dynamic)
HTML encoding (generic or specific)
efficiency
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Efficiency
CGI vs NSAPI, ISAPI (but proprietary
solutions)
Decrease process number (if large
number of clients) : multithreaded
gateway
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Transactions
transaction = DB program (read and
write sequence)
ACID properties
– A : Atomicity
– C : Consistency
– I : Isolation
– D : Durability
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Examples of transactional
services
on-line ordering (music, books, planes,
…)
bank
insurance
e-business!!!!
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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, ...)
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Transactions and cookies
Browser (client)
cgi
http server
1
1
1’ c1
2 c1
2’ c1, c2
3 fin c1, c2
5’ del(c1, c2)
1’ c1
2 c1
2’ c1, c2
3 fin c1, c2
5’ del(c1, c2)
4’ ok
1 : first access
4 sql(c1, c2)
1’ : c1 cookie is generated
2 : other access with c1 cookie transport
2’ : c1, c2 cookies are generated
3 : end of transaction with c1, c2 transport
4 : transaction is constructed and processed on the DBMS
5’ : cookies deletion
DBMS
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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)
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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)
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transactional gateway
browser (Client) http Server
Web and DB - INT Evry
cgi
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daemon gateway
DBMS
transactional gateway
principles
Context is managed by a daemon on
server-side
Need of a transaction id stored on clientside (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)
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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
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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
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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)
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Scripting language (serverside)
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
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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
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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
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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)
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Servlet Architecture
Web
browser
Client
HTTP
Server
Servlet container
servlet1
servlet2
Container manages servlets (activation, desactivation)
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Servlet object Model
session Object
request Object
servlet1
getParameter
getAttribute
getHeaders
getCookies
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getAttribute
Response Object
setBufferSize
setHeader
setRedirect
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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
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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>
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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
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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
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Personalized Tags
One can add his/her own tags to simplify
JSP page writing
tags libraries
mechanism to define new tags is
complex
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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>
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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
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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,...)
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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)
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Cocoon
Web browser
or PDA
Client
1
6
2
Apache
+ Tomcat
Cocoon
5
Doc.
XML
3
HTML Doc.
4 XSLT Interpreter
WML Doc.
PDF Doc.
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4 FOP Interpreter
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
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