2-1 WEB DATABSE INTERFACING Colorado Technical University IT420

2-2 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

2-3 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.

2-4 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.

2-5 HTML PAGE CONSTRUCT All HTML pages must make use of the following three tags: Indicates that this is an HTML file. Format is as follows: …your page…

2-6 HTML PAGE CONSTRUCT - Cont’d Used to specify the prologue of the file. Usually, only a title is placed in the head tag. Format is as follows: This is the title. ………...

2-7 HTML PAGE CONSTRUCT - Cont’d Used to bound remaining part of HTML document, e.g. text, links, JPGs, etc. Format is as follows: This is the title. ………...

2-8 Incorrect Nesting

2-9 HTML TITLE The 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.

2-10 HEADINGS Headings are used to divide sections of text. A maximum of six levels of headings can be used. Headings are of the form – –Heading Text –

2-11 Heading Examples

2-12 Paragraphs Paragraphs markers are used to indicate the beginning and end of a paragraph. Markers are as follows: – –paragraph text – –The closing tag is optional. The opening tag is required.

2-13 Page/URL links The format for a link is as follows: HREF=“../menu.html”>Go back to Main Menu Opening Tag File/URL to load when link is selected. Text that will be highlighted. Closing tag

2-14 HTML Forms Creating forms consists of two major steps: –Create the form layout –Handle the data (scripts, mail, etc.) Forms are created using the and tags Do not nest tags. It will not work.

2-15 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: – –…….. –

2-16 Submitting a Form Sample Form What is your name? Enter your Name:

2-17 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.

2-18 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.

2-19 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.

2-20 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.

2-21 VB CGI Example HTTP Client VB CGI Includes CGI32.BAS Access Database

2-22 Database Interface Methods Below are just some other ways to access databases: –Cold Fusion –HTML forms interfacing to CGI. –ODBC –Database Markup Language (DBML)

2-23 CGI Database Scripting Last but not least, SQL: SQL statements are embedded in the database markup language. This technique for generating a SQL statement for a database is proprietary to the vendor.

2-24 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.

2-25 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.

2-26 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 -. This is similar to linking to a CGI.

2-27 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.

2-28 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.

2-29 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. 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.

2-30 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.

2-31 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.

2-32 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.

2-33 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.

2-34 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.

2-35 Pop Quiz What components are needed for an HTML document? What is the difference between POST and GET forms?