1. Databases and DBMSs
Todd S. Bacastow
January 2005 1

2. Evolution

3. Ways of storing data Files (1960) (ancient times) Databases
Hierarchical (1970)
Network (1970)
Relational (1980)
Object (1990)

4. File terms Record Field File
data items related to a single logical entity (e.g. a student’s information) or row in a table
Field
a place for a data item in a record (first name field in a student record) or a column in a table
File
a sequence of records of the same type (the table)

5. File structures A file: “STUDENT” field ID Last First Grade
3 Smith Jane A
1 Wood Bob C
2 Kent Chuck B
4 Boone Dan B
record

6. File organization Serial Sequential new records appended
records ordered in file, usually according to a numeric key

7. File structures Serial
list of entries in which the order of entry into the list determines the order of the list
ID Last First Grade
3 Smith Jane A
1 Wood Bob C
2 Kent Chuck B
4 Boone Dan B

8. File structures
Search of a simple list entails going through each record until the query is satisfied (linear search), which is inefficient
ID Last First Grade
3 Smith Jane A
1 Wood Bob C
2 Kent Chuck B
4 Boone Dan B

9. File structures Sequential
list of entries ordered in some way (e.g. numerically or alphabetically)
ID Last First Grade
1 Wood Bob C
2 Kent Chuck B
3 Smith Jane A
4 Boone Dan B

10. File structures
ID Last First Grade
Search of an ordered sequential list can use a search method
1 Wood Bob C
2 Kent Chuck B
3 Smith Jane A
4 Boone Dan B

11. File structures
Indexes provide a reference to records based on an index field, which is ordered
Last Pointer
ID Last First Grade
Boone *
Kent *
Smith *
Wood *
1 Wood Bob C
2 Kent Chuck B
3 Smith Jane A
4 Boone Dan B

12. Problems with files Redundancy Inconsistency Maintenance problems
number of files grows with applications, and data is duplicated
Inconsistency
data is updated in one application’s files, but not in another’s
Maintenance problems
changes to data structures mean changes to many programs
Difficulty combining data
business needs may mean users want data from different applications

13. Other ways to organize Data model Other common models Hierarchical
A data model is a particular way of conceptually organizing multiple data files in a database
Other common models
Hierarchical
Network
Relational
Object

14. Network model

15. Network data model Relationships: one-to-one one-to-many many-to-one
Class
Relationships:
one-to-one
one-to-many
many-to-one
many-to-many
Student
Instructor
Grade ID
Department

16. Network data model Advantages Disadvantages flexible, fast, efficient
Complex
Restructuring can be difficult because of changing all the pointers

17. Hierarchical database model

18. Hierarchical data model
Class
Parent-child relationship:
one-to-one
one-to-many
Student
Instructor
Grade ID
Department

19. Hierarchical data model
Advantages
easy to search
add new branches easily
Disadvantages
Must establish the types of search prior to development of the hierarchical structure

20. Summary
Hierarchical and network data models have generally been replaced by the relational data model
Relational databases dominate the database market
Oracle
Informix
SQL Server
DB2
……..

21. Relational database model
Stores both
Data about real world objects (entities) in tables
Relationships between the tables

22. Relational database Fields (columns) in the table store attributes.
Each attribute has a specific domain.
Tuples (or records or rows) in the table store information.
Each tuple is a unique instance of an object.
Tables are composed of a set of tuples.
A table is also called a relation.

23. Terms Table Column Domain Row Primary Key
A collection of relevant data relating to one type of real world objects.
Column
A specific place for one type of data relating to one type of real world objects.
Domain
Set of all possible values for a specific column.
Row
Collection of data describing one real world object.
Primary Key
Columns, which are part of the row and uniquely identify any one row.

24. Records Each record represents a logical entity (e.g. a student)
Each field represents an attribute of the logical entity
Student
ID Last First Grade Class
1 Wood Bob C IST357
2 Kent Chuck B IST115
3 Smith Jane A IST357
4 Boone Dan B IST357

25. Keys
Each table has a primary key, one field (or a combination of fields) that has a unique value for each and every record in the table
Student
ID Last First Grade Class
ID is the primary key in this table (two students may share either a last or first name)
1 Wood Bob C IST357
2 Kent Chuck B IST115
3 Smith Jane A IST357
4 Boone Dan B IST357

26. Relating tables
Tables can be related (joined) together based on their keys
The idea is to decompose into separate tables with no redundancy and to provide a capability to reassemble with no information loss
Student
Class
ID Last First Grade Class
Name #Stud Instructor
1 Wood Bob C IST357
2 Kent Chuck B IST115
3 Smith Jane A IST357
4 Boone Dan B IST357
IST Jones
IST Brower
IST Fountain

27. Relating tables Student Class ID Last First Grade Class
Primary key
Foreign key
Primary key
Student
Class
ID Last First Grade Class
Name #Stud Instructor
1 Wood Bob C IST357
2 Kent Chuck B IST115
3 Smith Jane A IST357
4 Boone Dan B IST357
IST Jones
IST Brower
IST Mennis

28. Relating tables Student Class 1 Wood Bob C IST357
ID Last First Grade Class
Name #Stud Instructor
1 Wood Bob C IST357
2 Kent Chuck B IST115
3 Smith Jane A IST357
4 Boone Dan B IST357
IST Brower
IST Jones
IST Jones
Instructor
Name Office
Jones
Brower

29. DBMS Schema
Ultimately data in databases is stored in files, but their structure is hidden
Conceptual Schema
External Schema
Internal Schema
The view on data used by
application programs.
The logical model of data that is
separate from how it is used.
The physical storage of data in
files and indexes.

30. RDBMS Features Data Definition Language (DDL)
Data Manipulation Language (DML)
Integrity Constraints
Transaction Management
Concurrency
Security
Tuning of Storage

31. Data integrity and validation (Constraints)

32. Relationships Link between entities.
A relationship may define constraints.
E.G, a person can only have one SSN.

33. Advantages of RDBMS Eliminate unnecessary duplication of data
Enforce data integrity through constraints
Changes to conceptual schema need not affect external schema
Changes to internal schema need not affect the conceptual schema
Many tools are available to manage the database

34. Disadvantages of RDBMS
To store objects (e.g., drawings) in a relational database, the objects have to be ‘flattened’ into tables
e.g., a digital representation of a parcel must be separated from the behaviour of other parcels
Complex objects have to be taken apart and the parts stored in different tables
When retrieved from the database, the object has to be reassembled from the parts in different tables

35. Other Types of DBMS Object DBMS Object-relational DBMS
store objects as objects
designed to handle complex nested objects for graphical and multimedia applications
Object-relational DBMS
hybrid databases that can store data in tables but can also store objects in tables

36. Object DBMS
ODBMS have the advantage that objects can be stored directly
Object databases are closely linked to programming languages with ways of navigating through the database

37. Summary Common word Textbook word Alternate word Object word Table
Relation
File or Data set (old)
Object class
Column
Attribute
Field
Object field
Domain
Range of possible values
Datatype, subtype
Row
Tuple
Record
Object instance
Primary key
Key of the record
Object identifier