1. COMSATS INSTITUTE OF INFORMATION TECHNOLOGY, VEHARI
Data Models
COMSATS INSTITUTE OF INFORMATION TECHNOLOGY, VEHARI

2. Schemas and Instances
• Similar to types and variables in programming languages
• Schema
– the logical structure of the database
– Physical schema: database design at the physical level
– Logical schema: database design at the logical level
• Instance – the actual content of the database at a particular point in time

3. Database Schema • Is the description of a database
• It is specified during the database design and is not expected to change frequently.
• It is represented as a diagram called schema diagram.
– A schema diagram displays the structure of each record type but not the actual instance of a record.
• Each object in a schema is called a schema construct.

5. Database Instance
• A Database state or instance is the data in the database at a particular moment of time.
• Every update operation changes the database from one state to another.

7. Data models
• Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization
• Data Model comprises:
– A structural part
– A manipulative part
– Possibly a set of integrity rules
• Purpose
– To represent data in an understandable way

8. Types of Data models Hierarchical model Network model Relational model
Object relational model
Object oriented model

9. Data models 1- Hierarchical model: organizes data in a tree structure
Parent child relationship
2- Network model:

10. Data models 3- Relational model: Each row is unique
Each column has a unique name
Column values must be of same kind
4- object relational model:
complex objects such as time-series and geospatial data
diverse binary media such as audio, video, images, and applets

11. Data models 5- Object oriented model:
database functionality to object programming languages

12. Multi-user DBMS Architectures
• Teleprocessing
• File-Server
• Client-Server

13. Teleprocessing • Traditional architecture
• Single mainframe with a number
of terminals attached
• Trend is now towards
downsizing

14. File server
• File-Server is connected to several workstations across a network
• Database resides on file-server
• DBMS and applications run on each workstation
• Disadvantages includes:
– Significant network traffic
– Copy of DBMS on each workstation
– Concurrency, recovery and integrity control more complex

16. Client Server • Server holds the database and the DBMS
• Client manages user interface and runs applications
• Advantages include:
– Wider access to existing database
– Increased performance
– Reduction in communication costs
– Increased consistency

18. Keys
• A key is a combination of one or more columns that is used to identify rows in a relation
• A composite key is a key that consists of two or more columns
• A super key is a combination of columns that uniquely identifies any row within a relational database management system (RDBMS) table.