CIS 2336 Database Concepts

Knowledge is Power

• Data• Information = Processed or

organized data• Knowledge = Internally processed,

organized information

Measures of Data Quality

• Is it accurate?• Is it comprehensive?• Is it accessible?

Database Management Systems (DBMS)• Help ensure:

– data quality– accessibility

Database Models

• Flat file• Hierarchical• Networked• Relational• Object• Object-Relational• Document

Most Current Applications

• Implement the relational model

Relational Db Model

• Data arranged in tables– Each table has a column set that

contains a unique value for every row– Primary key

• Fixed set of columns– These represent entity attributes

• Data from different tables linked by logical relationships– These are called foreign keys

SQL – a Language for Querying a Database• Users access data using SQL

– Industry standard query language

Relational Theory

• Based on relational algebra and relational calculus

• Overarching principle: “reduce data redundancy to increase data integrity”

Structured Query Language

• ANSI 92 standards– Most major products comply with this

and provide extended functionality• ANSI 99 standards

– Extend traditional relational model closer to an object oriented model

Microsoft SQL Server

• ANSI SQL 92 compliant• Transact SQL

– Microsoft’s dialect of SQL– Has extensions to ANSI SQL 92

standard– Extensions are not accessible to all

other rdbms

Architecture of a SQL Server Db Interaction• User action in client application

calls a function in the application that generates a SQL query

• Query is generated in SQL language

Architecture of a SQL Server Db Interaction• Application uses a db access library

to communicate with SQL Server RDBMS– e.g., OLE DB or ODBC or SQL Server

Provider• Db access library translates request

into T-SQL commands

Architecture of a SQL Server Db Interaction• T-SQL commands encapsulated in

Tabular Data Stream (TDS) packets and passed to the db network library

• Client computer network library repackages TDS packets as network packets for transfer to the db server

• Packets transferred to server by network protocol (TCP/IP, e.g.)

Architecture of a SQL Server Db Interaction• Server extracts TDS packets from

network packets• TDS sent to Open Data Services on

the server where T-SQL commands are extracted

Architecture of a SQL Server Db Interaction• ODS sends the query to the SQL

Server relationship engine• SQL Server optimizes and executes

the query, working with the storage engine

• Relational engine creates result set of data and sends it to ODS

Architecture of a SQL Server Db Interaction• ODS creates TDS packets for client

application• Network library wraps TDS packets

in network protocol packets• Network library sends network

packets to client computer

Architecture of a SQL Server Db Interaction• Client network library extracts TDS

packets for database access library• From TDS packets, database

access library creates client compatible result set for client application

• Client application displays result set to end user

Performance Implications

• Client application sends only a database request to the server

• SQL Server sends only the result set to the client computer

• No server resources are used for user interactions

• No server resources used for data display

• No client resources used for query execution or data access

Performance Implications

• Client application design does not depend on what software drives the back end

• Client application does not depend on the network protocol used, thus the client application can be moved to a different network

Database Components (Objects)• Tables are the main db objects• Constraints – to guarantee data integrity

and consistency– Primary key, unique, check, default,

foreign key• Views – complex queries saved on the db

server• Indexes – speed up access to data• User-Defined functions and stored

procedures – save complex processes• Triggers – stored procedures that execute

based on a data event

SQL Server Security Model

• SQL Server login – give a user access to the SQL Server instance

• Database user – give a user access to a database

• Permissions – give a user permission to specific db objects and/or actions

• Roles – place a user into a predefined Server role or DB role

N-Tier Application Development

• Data tier – deals with the actual data the application uses

• Presentation tier – User interaction• Business tier – interacts with the

data tier to process data and then send processed results back to user through the presentation tier

CIS 2336

Database Concepts