Last edit: 05-03-17 Graham Wideman

Models

Assorted models for database access via web mechanisms.

Generic Superficial Model of Web-to-Database Application

Read-Only Application where URL (or Form data) includes parameters to generate on-demand database query, resulting in HTML table.

Examples:

• This is the classic CGI-gets-data-from-database scheme
• MS HTX/IDC

HTML-Based Application capable of Create/Read/Update/Delete transactions with database.

Examples:

• MS HTX/IDC
• MS ASP

Servlets (Web-Server-Helpers): Custom-coded all-in-one design

Implemented in PERL, C, VB etc

Servlet: Variants with different mechanisms for interacting with database.

A: Servlet understands particular flatfile formats
B: Servlet has driver(s) for local database
C: Servlet can interact with local or remote SQL database servers, either through native drivers, or via ODBC
D: Similar to C, except the complete kit includes database stored procedures to generate html documents (eg: Oracle WebServer).

MS HTX/IDC and MS ASP mechanisms are both varieties of B and C using Query Spec documents.  The main difference between HTX/IDC and ASP is that the former implements a simple and limited specification language, while ASP allows inclusion of Basic code to be executed by the ASP web-server-helper mechanism in making the query and composing the returned HTML document.

Applications with HTML pages that contain Components which can communicate with a server.

Examples:

• MS ADC?

Web server delivers stand-alone Applet to client; Applet communicates with Server

Generic Model for DB-savvy Applets

Applet provides visual display only

Examples:

• X-Term-like approaches
• Terminal-emulators

Applet provides visual display and field-level data management

Examples:

• Approaches using various J-Script or VB-Script plus Active-X or Java components?
• MS ADC? (ADC is clever in that it passes data to/from components packaged in HTML/MIME documents, possibly bypassing firewall issues).

Applet implements something like traditional client-server

Note: This is essentially "auto-installing database-Client/Server". The SQL connection may or may not require a "connection" component (like SQL*Net). JDBC drivers may cover this function.

Just one example of "Three Tier", combining two of the approaches above

Examples (of this particular 3-tier breakdown):

• Oracle Forms Web approach
• Citrix

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