Web databse interfacing
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WEB DATABSE INTERFACING. Colorado Technical University IT420. Web Database Software. HTTP - (Hyper Text Transfer Protocol) an application level protocol supporting platform-independent communications.

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Web databse interfacing

WEB DATABSE INTERFACING

Colorado Technical University

IT420


Web database software

Web Database Software

  • HTTP - (Hyper Text Transfer Protocol) an application level protocol supporting platform-independent communications.

  • URL - (Uniform Resource Locator) naming mechanism used by HTTP clients to access data - Contain:

    • Retrieval protocol, Internet node desired

    • File System directory, File name of resource to be served


Web database software contd

Web Database Software contd.

  • URL’s provide the naming scheme and location as well as the protocol needed to access the desired resource.

  • HTML - (Hyper Text Markup Language) hypertext and links combined into an ASCII text document that can be read by a Internet Browser.

  • The WEB has created the worlds largest set of “spaghetti code” to exist.


Web appeal

Web Appeal

  • The main appeal for the Web consists of two capabilities of the HTTP protocol:

    • Capability to transfer complex data types.

    • Ability to communicate among HTTP clients and other protocols using different gateways, e.g gopher, SMTP, etc.


Html page construct

HTML PAGE CONSTRUCT

  • All HTML pages must make use of the following three tags:

  • <HTML> Indicates that this is an HTML file. Format is as follows:

    • <HTML>

    • …your page…

    • </HTML>


Html page construct cont d

HTML PAGE CONSTRUCT - Cont’d

  • <HEAD> Used to specify the prologue of the file. Usually, only a title is placed in the head tag. Format is as follows:

    • <HTML>

    • <HEAD>

    • <TITLE>This is the title.</TITLE>

    • </HEAD>

    • ………...

    • </HTML>


Html page construct cont d1

HTML PAGE CONSTRUCT - Cont’d

  • <BODY> Used to bound remaining part of HTML document, e.g. text, links, JPGs, etc. Format is as follows:

    • <HTML>

    • <HEAD>

    • <TITLE>This is the title.</TITLE>

    • </HEAD>

    • <BODY>

    • ………...

    • </BODY>

    • </HTML>


Incorrect nesting

Incorrect Nesting

  • <HTML>

  • <HEAD>

  • <BODY>

  • </HEAD>

  • </BODY>

  • </HTML>


Html title

HTML TITLE

  • The <TITLE> tag is used to identify what the page describes.

  • This tag will also be used if someone saves the page as a bookmark.

  • Title can only contain plain text (No special markups allowed).

  • Since title is displayed in your browser, make it short so that it fits.


Headings

HEADINGS

  • Headings are used to divide sections of text.

  • A maximum of six levels of headings can be used.

  • Headings are of the form

    • <H1>

    • Heading Text

    • </H1>


Heading examples

Heading Examples


Paragraphs

Paragraphs

  • Paragraphs markers are used to indicate the beginning and end of a paragraph. Markers are as follows:

    • <P>

    • paragraph text

    • </P>

    • The closing tag </P> is optional. The opening tag <P> is required.


Page url links

Page/URL links

  • The format for a link is as follows:

    <A> HREF=“../menu.html”>Go back to Main Menu</A>

File/URL to load

when link is selected.

Text that will be highlighted.

Opening Tag

Closing tag


Html forms

HTML Forms

  • Creating forms consists of two major steps:

    • Create the form layout

    • Handle the data (scripts, mail, etc.)

  • Forms are created using the <FORM> and </FORM> tags

  • Do not nest <FORM> tags. It will not work.


Html forms cont d

HTML Forms - Cont’d

  • Form Tag consists of two attributes:

    • Method - This can be either GET or POST. This determines how form is handled by script.

    • Action - Usually a pointer to a script. This can also be a pointer to a URL or instructions to mail a message.

  • Format is as follows:

    • <FORM METHOD=POST ACTION=“http://www.myserver.com/cgi-bin/script.cgi”>

    • ……..

    • </FORM>


Submitting a form

Submitting a Form

<HTML><HEAD>

<TITLE> Sample Form</TITLE>

</HEAD><BODY>

<H2>What is your name?</H2>

<FORM METHOD=POST ACTION=“some action”>

<P>Enter your Name: <INPUT NAME=“theName”></P>

<P><INPUT TYPE=“SUBMIT” VALUE=“button name”></P>

</FORM>

</BODY></HTML>


Common gateway interfaces cgi

Common Gateway Interfaces (CGI)

  • CGI - (Common Gateway Interface) an interface that provides for running external programs to an HTML document.

  • Gateway programs are often scripting languages like VBScript and Javascript.

  • Programming language support can be Visual Basic, C++ or even Perl programs.

  • Environment variables are used to send parameters to the script program.


Cgi implementations

CGI Implementations

  • Two primary environment variables :

    • QUERY_STRING - anything following the first question mark in the URL accessing the gateway.

    • PATH_INFO - extra information embedded in the URL accessing the gateway.


Cgi implementations contd

CGI Implementations contd.

  • HTTP request/response transactions use four steps:

    • Open a connection to the server

    • Issue the request to the server

    • Receive the results from the server

    • Close the connection.

  • HTTP is a stateless system.


Cgi implementations contd1

CGI Implementations contd.

  • More complex methods can be setup for interaction with a server.

  • State information can be stored and passed between the client and server (Allows DB to maintain history).

  • State information can be appended to the results the client is passing the server.

  • The CGI script could open a database and keep it open during the session.

  • The CGI must track state, however.

  • States can also be tracked with cookies.


Vb cgi example

VB CGI Example

HTTP

Client

VB CGI

Includes CGI32.BAS

Access

Database


Database interface methods

Database Interface Methods

  • Below are just some other ways to access databases:

    • Cold Fusion

    • HTML forms interfacing to CGI.

    • ODBC

    • Database Markup Language (DBML)


Cgi database scripting

CGI Database Scripting

  • Last but not least, SQL:

  • SQL statements are embedded in the database markup language.

  • <DBQUERY Name=“Employees” Datasource=“EmployeeData” SQL=“SELECT * FROM dbEmployees WHERE EmpID = ‘#form.EID#’ “>

  • This technique for generating a SQL statement for a database is proprietary to the vendor.


Web server api s

Web Server API’s

  • Another way to access databases is with Server Applications Programming Interface (API) - native code proprietary to the Web server.

  • Best performance possible with server.

  • More difficult than CGI scripting, but much faster. Eliminates CGIs.

  • Supports - multithreading, process synchronization,error handling, and programming at protocol level.

  • Improperly written - can crash server.


Isapi api

ISAPI API

  • ISAPI applications for Microsoft IIS server utilize DLL’s loading at the same address space as the Web server for better performance.

  • Integrated with other Microsoft applications such as Back Office.

  • GetExtensionVersion() - entry point for ISAPI - returns version number of the DLL.

  • HttpExtensionProc() - is the entry point called for every client request.


Isapi api contd

ISAPI API contd.

  • WriteClient() or ServerSupportFunction() must then be called for a response to the client from HttpExtensionProc().

  • NSAPI - Netscapes server API cross-platform version works well as long as operating system calls are not made. NSAPI is more difficult.

  • The FORM tag links to the ISAPI DLL - <FORM ACTION= “http://207.217.22.134/scripts/amulet.dll” METHOD=????>. This is similar to linking to a CGI.


Internet database connector

Internet Database Connector

  • Provides ODBC access for HTTP requests on an IIS server.

  • Httpodbc.dll - the IDC ISAPI dll for ODBC database access.

  • Two types of files control access:

    • .idc - contains necessary information to connect to he database.

    • .htx - HTML template for the file returned to the browser. ASP replaces this functionality.


Server side includes

Server Side Includes

  • Allows small amounts of dynamic data to be inserted into an HTML document.

  • Costs a fair amount of server resources.

  • Tags are embedded into the HTML document and read by the server side implementation.

  • A typical example of an SSI is a web counter.


Server side includes cont d

Server Side Includes - Cont’d

  • SSI requires high overhead (CPU and memory) because web server has to scan through entire HTML doc to find SSI commands.

  • SSI was founded as freeware.

  • <!--#SSIcommand tag1=“value1” tag2=“value2” -->

  • SSI commands are ignored by non SSI capable servers because of the comment line. SSI aware servers will pick these up.

  • This is a non-standard HTML document.


Server side include commands

Server Side Include Commands

  • SSI consists of six commands:

    • CONFIG

    • INCLUDE

    • ECHO

    • FSIZE

    • FLASTMOD

    • EXEC

  • A product called WebQuest has added some additional commands to SSI.


Java database connections

Java Database Connections

  • Java Applets connect to a database using API’s provided by the vendor (native) or utilizing JDBC (a common API layer in Java).

  • JDBC lets you hide the specifics of your database from the application.

  • JDBC is platform independent.

  • DAO is available for use in the windows environment to interface J++ with Access.


Active server activex

Active Server & ACTIVEX

  • Active server scripting executes completely on the server and is based on VB scripting language.

  • ACTIVEX controls execute on the server and return requested information in the HTML stream mixed with the regular HTML.


Active server activex cont d

Active Server & ACTIVEX - Cont’d

  • The following occurs when an ASP is first read by the server:

    • HTML and Client side scripting code found on page is passed to the browser.

    • If server-side script code is found, it runs on the server instead of being passed back to the browser.

  • The browser does not know that page was created dynamically, it just displays the HTML.


Activex data objects

ActiveX Data Objects

  • ADO is an ACTIVEX Component module that utilizes the new OLE DB technology. Making remote objects look local.

  • ADO is the data access component of ASP.

  • ADO allows you to independently create objects where DAO and RDO require a hierarchy to be created for objects.

  • ADO allows you to have build an object based interface.


Pop quiz

Pop Quiz

  • What components are needed for an HTML document?

  • What is the difference between POST and GET forms?


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