1. Introduction to Database Systems
Purpose of Database Systems
Views of Data
Data Models
Data Definition Language
Data Manipulation Language
Transaction Management
Storage Management
Database Administrator
Database Users
Overall System Structure
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2. Database Management System (DBMS)
Collection of interrelated data
Set of programs to access the data
DBMS contains information about a particular enterprise
DBMS provides an environment that is both convenient and efficient to use.
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3. Purpose of Database Systems
Difficulties in conventional file-processing systems: (DBMS attempts to solve)
Data redundancy and inconsistency
Difficulty in accessing data
Data isolation -- multiple files and formats
Integrity problems
Atomicity of updates
Concurrent access by multiple users
Security problems
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4. View of Data …... View level View 1 View 2 View n Logical level
Physical level
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5. Levels of Abstraction
Physical level: describes how a record (eg.: customer) is stored in terms of block#, sector#, byte# etc.
Logical level: describes data stored in database, and the relationship among the data:
typedef struct customer {
string name;
string street;
integer city; }
View level: Application programs/GUI etc hide the actual representation and present only the required data in a convenient way. Eg: Visual forms, graphical forms.
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6. Instances and Schemas
Schema is a description and an instance is a set of data that fits the description.
Schema : logical structure of the database (eg. Set of customers and accounts and the relationship between them)
Instance : actual content of the database at a particular point in time.
One schema may have many instances.
Analogy : type and variable in a programming language.
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7. Data Independence
Ability to modify a schema definition in one level without affecting a scheme definition in the next higher level.
Interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others:
Two levels of data independence:
Physical data independence
Logical data independence
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8. Data Models A collection of representations for describing:
data, data relationships, data semantics, data constraints
Object-based logical models
Entity-Relationship (ER) model
Object-oriented model
Semantic model
Functional model
Record-based logical models
Relational model (e.g. SQL/DS, DB2)
Network model
Hierarchical Model
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9. Entity-Relationship Model
street
SSN
number
balance
city
name
customer
depositor
account
entity
attribute
relationship
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10. Relational Model Customer Table Name SSN street city account no.
Johnson
Alma
Palo Alto
A-101
Account Table
Account No.
Balance
A-101
500
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11. Data Definition Language (DDL)
Specification notation for defining database scheme
DDL compiler generates a set of tables in a data dictionary
Data dictionary contains metadata (data about data)
Data storage and definition language - special type of DDL in which storage and access methods used by the dbms are specified.
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12. Data Manipulation Language
Language for accessing and manipulating the data organized by appropriate data model
Two classes of languages:
Procedural - user specifies what data is required and how to get those data
Non-procedural -- user specifies what data is required without specifying how to get those data
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13. Transaction Management
A transaction is a collection of operations that perform a single logical function in a database application
Example: Withdraw $100 from Acct Number A-101
Verify the balance
Update account table (& other tables)
Deliver money
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14. Transaction Management (contd.)
Transaction-management component ensures that the db remains in a correct state despite system failures (e.g. power failures and operating system crashes) and transaction failures.
ACID property: Atomicity, Consistency, Isolation, Durability
Concurrency-control manager controls the interaction among the concurrent transactions.
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15. Storage Management
A storage manager provides the interface between the low-level data and the application programs and queries submitted to the system.
The storage manager is responsible for the following tasks:
interaction with file-manager
efficient storing, retrieving, and updating of data
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16. Overall System Structure
Naïve users
Application
programmers
Sophisticated
users
DBA
Application
interfaces
programs
query
Database scheme
Query processing
DBMS
System
Object code
Embedded
DML compiler
DML
compiler
DDL
interpreter
Query evaluation
engine
Storage manager
Transaction
manager
Buffer manager
File manager
Data dictionary
Statistical data
indices
Data files
Disk
storage
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17. Database Administrator
Coordinates all the activities of the database system;
DBA should have a good understanding of the enterprise’s information resources and needs.
DBA’s duties include:
Scheme definition
Storage structure and access method definition
Granting user authority to access the database
Specifying integrity constraints
Acting as liaison with users
Monitoring performance and responding to changes in requirements
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18. Database Users Differentiated by the how they interact with the system
Naïve users: invoke pre-determined application with high-level user interface
Application programmers; Use DML calls, embedded calls
Sophisticated users: managers, decision support systems: request using query languages
Specialized users: design and write specialized applications.
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