DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson Database Middleware

• Early client/server database systems

– Two tier

– Server does business logic (data analysis & report generation)

– Server does database logic

– Client communicates directly with database on the server

– Client does data formatting and display

– Primitive middleware is simply for enabling communication

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson Database middleware

• Business logic – data analysis and report generation takes place on client

• Data is needed at the client

• Server logic to selectively extract needed data from tables for transmission to client – not entire files

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson SQL

• Structured Query Language

• ANSI standard American National Standards Institute

• Standard allows interoperability

Provides

• Create & modify tables and databases

• Add, delete, modify and manipulate data

• Query

• Interfaces through programming languages

• Vendors provide enhanced features not part of ANSI SQL

– Competitive advantage

– Compromises transparent interoperability

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson SQL processing

1. Application generates SQL query

2. Query goes to client middleware

3. Query is passed (through layers) across network

4. Server middleware submits query

5. Database interprets query – result is a dataset

6. Dataset is transmitted across network to client middleware

7. Data is presented to the client application

Final execution of query is on the local dataset

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson Proprietary API

• Most database vendors provide a proprietary API to link to their database platform (Oracle uses SQL*NET)

• Applications then become bound to a particular database

• Separate application versions needed for different databases

• One solution – a universal API translator into a specific API

• Microsoft ODBC – Open Database Connectivity

• Provides a set of non-database specific APIs

• Layer inserted between client application and middleware

• What about interfacing to multiple databases?

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson ODBC

Client Application

Oracle SQL*NET

NOS

Physical NW Layers

Oracle Server

Oracle SQL*NET

NOS

Physical NW Layers

ODBC

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson 3 Tier ODBC

Oracle Server

Oracle SQL*NET

NOS

Physical NW Layers

Client Application

Client Middleware

NOS

Physical NW Layers

SequelLink

SQL*NET

NOS

Physical NW Layers

Sybase API

Sybase Server

Sybase mid-ware

NOS

Physical NW Layers

ClientMiddle-ware

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson Universal Data Access

• An alternative solution (newer)

• OLE DB: Object Layering and Embedded Database API

• Inserts another layer of middleware on the server side

• Clients generate OLE DB rather than a proprietary API or SQL

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson OLE DB

Client Application

Client Middleware

OLE

NOS

Physical NW Layers

SQL Database

ODBC

NOS

Physical NW Layers

OLE DB Client

SQL Database

ODBC

NOS

Physical NW Layers

OLE DB Client

DB MidWareCSIS 4490 N-Tier Client/ServerDr. Hoganson Web Middleware

• Middleware to make the application browser-compatible

• Development environments

• Examples

– ActiveX

– Java

– CGI (Common Gateway Interface)