1. Ch1: File Systems and Databases Hachim Haddouti
Database Systems
Ch1: File Systems and Databases
Hachim Haddouti

2. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Agenda
Motivation
History
File Systems
Database Systems
Data models
Summary
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

3. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Why Database?
DBMS contains information about a particular enterprise
DBMS provides an environment that is both convenient and efficient to use.
Database Applications:
Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grades
Sales: customers, products, purchases
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

4. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
History
File systems
Pre-relational Databases
Relational Databases
Post-relational Databases
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

5. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
History (cont.)
Pre-relational DB (70)
First distinction between logical and physical data management
Data management becomes important.
Need of data models
Relational Database Systems (80)
No redundancy in data storage
Integrated data control even by distributed data storage
Multiuser operation and high performance
Post-relational Databases (90)
objectoriented Databases
Multidimentional Databases
Datawarehouses
Distributed databases
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

6. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
A Simple File System
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

7. Drawbacks of file Systems
To retrieve data from a file system, extensive programming is often needed in a 3GL - both what and how are programmer’s responsibility
Ad hoc queries (spur-of-the-moment questions) become impossible
Each file must have its own file-mgt. system to create the file structure, add data to file, delete data from it, modify it and list its contents
All data access programs are subject to change when the file structure changes (e.g., a field is deleted or its position is changed)
Structural dependency
Even a change in the data type of a field (e.g., integer to real) requires all data access programs to change
Data dependency
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

8. Purpose of Database System
In the early days, database applications were built on top of file systems
Drawbacks of using file systems to store data:
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation — multiple files and formats
Integrity problems
Integrity constraints (e.g. account balance > 0) become part of program code
Hard to add new constraints or change existing ones
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

9. Purpose of Database Systems (Cont.)
Drawbacks of using file systems (cont.)
Atomicity of updates
Failures may leave database in an inconsistent state with partial updates carried out
E.g. transfer of funds from one account to another should either complete or not happen at all
Concurrent access by multiple users
Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
E.g. two people reading a balance and updating it at the same time
Security problems
Database systems offer solutions to all the above problems
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

10. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
DBMS vs. File Systems?
Database consists of logically related data stored in a single repository
Provides advantages over file system management approach
Eliminates inconsistency, data anomalies, data dependency, and structural dependency problems
Stores data structures, relationships, and access paths
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

11. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Levels of Abstraction
Physical level describes how a record (e.g., customer) is stored.
Logical level: describes data stored in database, and the relationships among the data.
type customer = record name : string; street : string; city : integer; end;
View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes.
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

12. View of Data An architecture for a database system
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

13. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
DBMS Functions
Data dictionary: stores data relationships to be consulted by all programs that access the database; automatically records changes
Structural and data dependencies are eliminated
Interaction with the file manager: takes care of structures for data storage
Security: enforces data access policies
Multi-user access control
Backup and recovery
Data integrity
Data access through 4GL and 3GL’s
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

14. Types of Database Systems
Number of Users
Single-user (Desktop database)
Multi-user (Enterprise database)
Location
Centralized
Distributed
Use
Transactional (Production)
Decision support
Data warehouse
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

15. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Database Models
A database model is a collection of logical constructs used to represent the data structure and the data relationships found within the database.
Two Categories of Database Models
Conceptual models focus on the logical nature of the data representation. They are concerned with what is represented rather than how it is represented.
Implementation models place the emphasis on how the data are represented in the database or on how the data structures are implemented.
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

16. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Database Models
Three Types of Relationships
One-to-many relationships (1:M)
A painter paints many different paintings, but each one of them is painted by only that painter.
PAINTER (1) paints PAINTING (M)
Many-to-many relationships (M:N)
An employee might learn many job skills, and each job skill might be learned by many employees.
EMPLOYEE (M) learns SKILL (N)
One-to-one relationships (1:1)
Each store is managed by a single employee and each store manager (employee) only manages a single store.
EMPLOYEE (1) manages STORE (1)
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

17. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Database Models
Three Types of Implementation Database Models
Hierarchical database model
Network database model
Relational database model
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

18. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
A Hierarchical Structure
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

19. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Hierarchical Model
Advantages
Conceptual simplicity
Database security
Data independence
Database integrity
Efficiency dealing with a large database
Disadvantages
Complex implementation
Difficult to manage
Lacks structural independence
Applications programming and use complexity
Implementation limitations
Lack of standards
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

20. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Child with Multiple Parents
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

21. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
A Network Database Model
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

22. Network Database Model
Advantages
Conceptual simplicity
Handles more relationship types
Data access flexibility
Promotes database integrity
Data independence
Conformance to standards
Disadvantages
System complexity
Lack of structural independence
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

23. Relational Database Model
Basic Structure
RDBMS allows operations in a human logical environment.
The relational database is perceived as a collection of tables.
Each table consists of a series of row/column intersections.
Tables (or relations) are related to each other by sharing a common entity characteristic.
The relationship type is often shown in a relational schema.
A table yields complete data and structural independence.
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

24. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Linking Relational Tables
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

25. Relational Database Model
Advantages
Structural independence
Improved conceptual simplicity
Easier database design, implementation, management, and use
Ad hoc query capability (SQL)
Powerful database management system
Disadvantages
Substantial hardware and system software overhead
Possibility of poor design and implementation
Potential “islands of information” problems
DBMS, Ch1 File Systems and Databases, Hachim Haddouti

26. DBMS, Ch1 File Systems and Databases, Hachim Haddouti
Summary
File systems
History
DBMS
Data models
DBMS, Ch1 File Systems and Databases, Hachim Haddouti