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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
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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
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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
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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
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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?
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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
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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
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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
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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
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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)