The document defines key concepts related to databases including data, database, DBMS, database system, and data model. It describes hierarchical, network, and relational database models. The hierarchical model logically represents data as an upside down tree with each parent having many children and each child only one parent. The network model resembles the hierarchical model with a collection of records in one-to-many relationships. The relational model represents data as relations or tables with rows and columns where each cell contains a single value.

5. Basic DefinitionsBasic Definitions
 Data: Known facts that can be recorded and have an implicit
meaning.
 Database: A collection of related data
 Database Management System (DBMS): A software
package/ system to facilitate the creation and maintenance of
a computerized database.
 Database System: The DBMS software together with the
data itself. Sometimes, the applications are also included.

6. DBMSDBMS
A DBMS consists of a group of
programs that manipulate the database and
provide an interface between the database ,
the user of the database and other
application programs.

7. What is Data ModelWhat is Data Model
Data Model: A set of concepts to describe the
structure of a database, and certain constraints
that the database should obey.

8. Hierarchical DB modelHierarchical DB model
Logically represented by an upside down TREE
Each parent can have many children
Each child has only one parent
The top layer is perceived as the parent of the
segment directly beneath it.
The segments below other segments are the children
of the segment above them.
SALIENT FEATURES

9. Hierarchical DB modelHierarchical DB model

10. ExampleExample
Emp No. First Name Last Name Dept Num
100 John Dougals 2A
101 Antony Wanton 2B
102 Mary Queen 2C
103 David Moorey 2D
Serial No. Type User Emp No.
3009734-4 Computer 100
3-23-283742 Monitor 101
2-22-723423 Monitor 102
232342 Printer 103
PARENT
CHILD

11. AdvantagesAdvantages
 Conceptual simplicity
 Data independence
 Efficiency dealing with a large database

12. DisadvantagesDisadvantages
 Complex implementation
 Difficult to manage and lack of standards
 Lacks structural independence
 Applications programming and use complexity
 Implementation limitations (no M:N relationship)

13. The Network ModelThe Network Model

14. The Network Model (continued)The Network Model (continued)
Schema
◦ Conceptual organization of entire database as viewed
by the database administrator
Subschema
◦ Defines database portion “seen” by the application
programs that actually produce the desired
information from data contained within the database
Data Management Language (DML)
◦ Defines the environment in which data can be
managed

15. Schema Data Definition Language (DDL)
◦ Enables database administrator to define
schema components
Subschema DDL
◦ Allows application programs to define
database components that will be used
DML
◦ Works with the data in the database

16. Resembles hierarchical model
Collection of records in 1:M relationships
Set
◦ Relationship
◦ Composed of at least two record types
 Owner
 Equivalent to the hierarchical model’s parent
 Member
 Equivalent to the hierarchical model’s child

17. The Network Model (continued)The Network Model (continued)

18. The Network Model (continued)The Network Model (continued)
Disadvantages
◦ Too cumbersome
◦ The lack of ad hoc query capability put heavy
pressure on programmers
◦ Any structural change in the database could
produce havoc in all application programs that
drew data from the database
◦ Many database old-timers can recall the
interminable information delays

19. Relational DB modelRelational DB model

20. Relational DB modelRelational DB model

21. Relation subject to the following rulesRelation subject to the following rules
Relation (file, table) is a two-dimensional table.
Attribute (i.e. field or data item) is a column in the
table.
Each column in the table has a unique name within
that table.
Each column is homogeneous. Thus the entries in any
column are all of the same type (e.g. age, name,
employee-number, etc).
Each column has a domain, the set of possible values
that can appear in that column.
A Tuple (i.e. record) is a row in the table.

22. Relation subject to the following rulesRelation subject to the following rules
 The order of the rows and columns is not important.
 Values of a row all relate to some thing or portion of a thing.
 Repeating groups (collections of logically related attributes
that occur multiple times within one record occurrence) are not
allowed.
 Duplicate rows are not allowed (candidate keys are designed to
prevent this).
 Cells must be single-valued (but can be variable length). Single
valued means the following:
◦ Cannot contain multiple values such as 'A1,B2,C3'.
◦ Cannot contain combined values such as 'ABC-XYZ' where
'ABC' means one thing and 'XYZ' another

23. Thank You