1. Database System Concepts and Architecture
Chapter 2
COSC 457
Sungchul Hong

2. The architecture of DBMS
Early monolithic system
Modular design
Client module
Server module
Storage, access, search, and other functions

3. Data Models, Schemas, and Instances
A collection of concepts that can be used to describe that structure of a database.
Structure of a database: data types, relationships, and constraints
Basic operations
Specifying retrievals and updates on the database
Dynamic aspect (behavior): user defined operations.

4. Categories of Data Models
High-level (conceptual) Data Models
They provide concepts that are close to the way many users perceive data.
Representational (Implementation) Data Models
Between two extremes
Low-level (physical) Data Models
They provide concepts that describe the details of how data is stored in the computer.

5. Conceptual Data Model Entities, attributes, and relationships
Entity represents a real-world object or concept.
An attribute represents some property of interest that further describes an entity.
A relationship among two or more entities represents an interaction among the entities.
Entity-Relationship model.

7. Representational Data Models
Relational data model
Network models
Hierarchical models
Object data models

8. Hierarchical Model ADVANTAGES: DISADVANTAGES:
Hierarchical Model is simple to construct and operate on
Corresponds to a number of natural hierarchically organized domains - e.g., assemblies in manufacturing, personnel organization in companies
Language is simple; uses constructs like GET, GET UNIQUE, GET NEXT, GET NEXT WITHIN PARENT etc.
DISADVANTAGES:
Navigational and procedural nature of processing
Database is visualized as a linear arrangement of records
Little scope for "query optimization"

9. Network Model ADVANTAGES: DISADVANTAGES:
Network Model is able to model complex relationships and represents semantics of add/delete on the relationships.
Can handle most situations for modeling using record types and relationship types.
Language is navigational; uses constructs like FIND, FIND member, FIND owner, FIND NEXT within set, GET etc. Programmers can do optimal navigation through the database.
DISADVANTAGES:
Navigational and procedural nature of processing
Database contains a complex array of pointers that thread through a set of records. Little scope for automated "query optimization”

10. Network Model

11. Relational Data Model Advantages Disadvantage
Strong Mathematical background
Query optimization is possible
4th generation language (non-procedural)
Disadvantage
Some (e.g. joint) Operations require a great amount of resources.

12. Relational Data Model N
Branch
Work 1
Staff

13. Physical Data Models
How data is stored in the computer by representing information such as record formats, record orderings, and access paths.

14. Schemas, Instances, and Database State
Schema (Meta data, intension)
The description of the database
It is specified during database design.
It is not expected to change frequently.
Schema diagram: names of record types and data items
Instances (extension of the schema)
The actual data in a database
It may change quite frequently.
Database state: a snapshot, current set of instances
DBMS is responsible for ensuring that every state of the database is a valid state.

15. Schema
Instance

17. DBMS Architecture and Data Independence
The Three-Schema Architecture
Internal level
Conceptual level
External level
Data Independence
Logical data independence
Physical data independence

18. The Three-Schema Architecture
Internal level (internal schema)
Physical storage structure of the database.
Conceptual level (conceptual schema)
The structure of the whole database for a community of users.
Hides details
External (view) level (external schemas or user views)
User’s view point of a database.
Mappings: transforming requests and results between levels

20. Data Independence Logical data independence Physical data independence
Capacity to change the conceptual schema without having to change external schemas or application programs.
Physical data independence
Capacity to change the internal schema without having to change to conceptual (or external) schema.
Only mappings between two levels will be changed.

21. DBMS Languages Data Definition Language (DDL)
Storage Definition Language (SDL)
View Definition Language (VDL)
Data Manipulation Language (DML)
Comprehensive database language  SQL
Nonprocedural DML
Interactive (query language) or embedded (host/data)
Set-at-a-time, set-oriented, declarative (what)
Procedural DML
Embedded in a general-purpose programming language.
Record-at-a-time,

22. SQL Example (DDL)
CREATE TABLE DEPT ( DNAME VARCHAR(10) NOT NULL, DNUMBER INTEGER NOT NULL, MGRSSN CHAR(9), MGRSTARTDATE CHAR(9), PRIMARY KEY (DNUMBER), UNIQUE (DNAME), FOREIGN KEY (MGRSSN) REFERENCES EMP ON DELETE SET DEFAULT ON UPDATE CASCADE );

23. SQL Example (DML)
SELECT BDATE, ADDRESS FROM EMPLOYEE WHERE FNAME='John' AND MINIT='B’ AND LNAME='Smith’;

24. SELECT staffNo, fName, lName, position, salary FROM Staff
sex
DOB
salary
branchNo
SL21
John
White
Manager M
Oct/1/45
30000
B005
SG37
Ann
Beech
Assistant F
Nov/10/60
12000
B003
SG14
David
Ford
Supervisor
Mar/24/58
18000
SA9
Mary
Howe
19/Feb/70
9000
B007
SG5
Susan
Brand
Jun/3/40
24000
SL41
Julie
Lee
Jun/13/65
SELECT staffNo, fName, lName, position, salary
FROM Staff
WHERE salary > 10000;

25. DBMS Interfaces Menu-Based Interfaces for Browsing.
Browsing interface
Forms-Based Interfaces
Forms specification languages
Graphical User Interfaces
Natural Language Interface
Interfaces for Parametric Users
Bank tellers
Interfaces for the DBA: privileged commands
Creating accounts, setting system parameters, granting account authorization, changing a schema, …

26. DBMS Component Modules
Operating systems
Stored Data Manager
DDL compiler
Stores description of the schemas in the DBMS catalog.
Names of files, data items, storage details of each file, mapping in formations among schemas, constraints
Run-time database processor
Query compiler: interactive queries
Pre-compiler: DML command from an application program
DML compiler: compilation into object code.

28. Embedded Code (Java) try {
rset= stmt.executeQuery("SELECT * from department");
ResultSetMetaData rsmd=rset.getMetaData();
while (rset.next())
{ System.out.println(" " + rset.getString(1) + " " + rset.getString(2) +
" " + rset.getString(3) +" "); }

29. Interactive SQL SQL> SELECT table_name FROM user_tables; TABLE_NAME
DEPARTMENT
STUDENT

30. Database Systems Utilities
Loading
Convert non-database files into db files
Backup
File reorganization
organize a database file into a different file organization to improve performance
Performance monitoring
Monitoring database usage.
Sorting files, data compression, etc.

31. Tools, Application Environments, and Communication Facilities
Expanded data dictionary system
Usage standards, application program descriptions
Application development environment
Communications software

32. Classification of Database
Data model
Relational data model, Object data model, Hierarchical, Network
Number of users
Single-user (Access) , multi-user systems (Oracle)
Number of sites
Centralized, distributed
Costs
Types of Access path
Target area
General purpose, special purpose (on-line transaction processing system)