Download Client-server database systems and ODBC

Client-server database
systems and ODBC
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
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Client-server architecture and
components
More on reliability and security
ODBC standard
Database processing functions
The client-server architecture
The network “cut” is between
applications and the DBMS
 Database processing is on the server

DBMS Driver
Receive processing requests from
applications
 Format requests and deliver to DBMS
 Receive responses from DBMS
 Format responses for application
 Communication layer on client and
server to exchange messages between
DBMS and driver
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Roles of client and server
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Client

» Manage the user
interface
» Enforce business
rules
» Process application
logic
» Generate database
requests (SQL)
» Transmit database
requests to server
» Receive results from
server
» Format results
Server
» Accept database request from
clients
» Process database requests
» Format results and transmit to
client
» Enforce business rules
» Perform integrity checking
» Maintain database overhead
data
» Provide concurrent access
control
» Provide recovery and security
services
Advantages & disadvantages

Pro
» Applications use client CPUs in parallel
– More powerful applications
» Network traffic is reduced
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Con
» Concurrency control
» Multiple client OS’s
Multithreading
Client requests
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Native library calls (API)
» DBMS-specific
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Embedded SQL
» Static SQL
– SQL structure fixed at compile time
– Faster
» Dynamic SQL
– SQL structure determined at run time
– More flexible
Business rules:
client-enforcement
Business rules:
server-enforcement
Enforcement of business rules

Client
» Triggers
» Duplication
» What about using DML directly?

Server
» All in one place
» What if DBMS cannot enforce business
rules?
Concurrency control
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Pessimistic locking
» Assume things will go wrong
» Prevent problems all the time
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Optimistic locking
» Assume things will go well
» If problem, do it over
Pessimistic locking:
same page, different records
Optimistic locking:
same page, different records
What if same record?
Concurrency control, take 2

Pessimistic versus optimistic locking,
which is better?
» Depends on application...
» What is the common case?
– If conflict is frequent, use pessimistic!
– If conflict is rare, use optimistic!
ODBC
Open DataBase Connectivity
 Industry-standard interface between
client applications and server DBMS
products
 The idea is to write DBMS-independent
applications, as long as they conform to
the ODBC standard
 To conform or not to conform?
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ODBC architecture
ODBC components
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On the server:
» Data source(s) - database, DBMS, OS,
network platform
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On the client:
» DBMS drivers - one per data source
– Receive ODBC request
– Process if not standard SQL
– Submit to specific data source
» Driver manager - one per client
– Receive ODBC request from application
– Load appropriate driver and forward request
ODBC drivers
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Single-tier: process both ODBC calls
and SQL statements
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Multiple-tier: process ODBC calls and
pass SQL statements to data source
ODBC conformance levels

3 levels of driver API conformance
» Core (connect, commit/rollback, error...)
» Level 1 (partial results, catalog, driver
gestalt...)
» Level 2 (browse, scrollable cursors...)

3 levels of SQL conformance
» Minimum (simple select, create, drop, insert,
update, delete, simple expressions...)
» Core (indices, views, grant, revoke, subqueries, aggregate functions...)
» Extended (outer joins, cursors, scalar
functions, procedures...)