1. The Relational Data Model
Lecture 02
The Relational Data Model

2. Advantages of Database

3. Advantages of Database
Data Consistency
Better Data Security
Faster Application Development
Economy of Scale
Better Concurrency Control
Better Backup and Recovery Facility

4. The Range of Database Applications
Personal Database – standalone desktop database
Workgroup Database – local area network (<25 users)
Department Database – local area network ( users)
Enterprise Database – wide-area network (hundreds or thousands of users)

5. Evolution of DB Systems
Flat files s s
Hierarchical – 1970s s
Network – 1970s s
Relational – 1980s - present
Object-oriented – 1990s - present
Object-relational – 1990s - present
Data warehousing – 1980s - present
Web-enabled – 1990s - present

6. Models, Schemas and States
A data model defines the constructs available for defining a schema
defines possible schemas
A schema defines the constructs available for storing the data
defines database structure
limits the possible database states
A database state (or instance) is all the data at some point in time
the database content

7. Models, Schemas and States
data model
fixed by the DBMS
Defined by DB designer
schema
defined by the DB designer
generally fixed once defined *
database state
changes over time due to user updates
* schema modifications are possible once the database
is populated, but this generally causes difficulties

8. Relation Schemas and Relation Instances

9. Relation Schemas
A relation is defined by a name and a set of attributes
Each attribute has a name and a domain
a domain is a set of possible values
all domains are sets of atomic values
RDM does not recommend complex data types
domains may contain a special null value

11. Definition: Relation Schema
R is the relation name
A1 … An are the attribute names
Domains are denoted by
degree = the number of attributes
R(A1, A2, … , An)
dom(Ai)

12. Characteristics of Relations
A relation is a set
tuples are unordered
no duplicate tuples
Attribute values within tuples are ordered
values are matched to attributes by position

13. Characteristics of Relations
Values in tuples are atomic
Each Column has distinct name
The values of the attribute come from the same domain
The order of the column is immaterial
Each row/tuple/record is distinct

14. SQL: Relation States A relation is viewed as a table
The attributes define the columns of the table
Each row in the table holds related values for each attribute
a row often represents a conceptual entity (object)
Values in each column must come from the domain of the attribute

15. Example Schema