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Unit 1: Introduction to Database Outline - Coggle Diagram
Unit 1: Introduction to Database Outline
1.1 Evolution of Database System
Database:
kind of
electronic filing cabinet
collection of
computerized data files
Database System:
( collection of application programs that interact with database)
computerised record keeping system
to
store information
and allow users to
retrieve and update information
on demand
4 major components of Database System:
Hardware:
Personal computer, computer networking, magnetic disk, I/O devices
Software:
Database Management System, application programmes(
C, C++, Visual Basic)
, operating system.
Data
People/User:
Application programmers, end-users and database administrators
Database Management System(DBMS)
computer software
used to manage the databases.
to create, maintain and provide controlled access to these databases.
Eg.
Microsoft SQL Server, MySQL, Microsoft Access and Oracle
1.2 Database Environment
3 levels of architecture of a DBMS:
1. External level
user logical level
closest to users
concerns the way the data is seen by individual users
2. Conceptual level
community logical level
level of indirection between external level and internal level
3. Internal level
storage level
closest to the physical storage
concerns the way the data is stored inside the system
Conceptual Level
representations of the entire information content of the database
concentrates on describing all entities, relationship, attributes, data types, user operations and constraints.
External / Conceptual Mapping
correspondence between a particular external view and the conceptual view.
enable DBMS to maps names in the user's view on the relevant part of the conceptual schema
Internal / Conceptual Mapping
conceptual view and the stored database
specifies how conceptual records and fields are represented at the internal level
External Level
individual user views
see only particular information form databases that are interested
hides the rest of the database form that user group
Internal Level
describes the complete details of data storage and access paths of the database
contain the definitions of stored records, methods of representation, data fields indexes, and storage strctured used
Database Languages
Data Definition Language (DDL)
used by
database administrator
and
database designers
define schema or modify the existing schema
allows user to specific the data types and structure and the constraints on the data to be stored in the database
Data Manipulation Languages (DML)
used to manipulate the database (
retrieve, insertion, deletion and modification
)
Data Control Languages (DCL)
used to control the
security
and
permission to access
the data
Component of DBMS
DML Compiler
extract the DML commands from the application program
converted into appropriate program object codes for database access
DML compiler must interact with the query processor to generate the object codes
Query Processor
transform high-level SQL into correct execution strategy expressed in a low-level instruction directed to the database manager
DDL Compiler
stores the description of the schema in the system catalogue
Database Manager
interfaces with user-submitted application programs and queries
determine what conceptual records are required to satisfy the request
Client-server architecture
Two-tier
(slower)
1. First-tier(client)
handles the user interface and the business and data application logic
2. Second-tier(Database server)
handles the database and the transaction logic
Three-tier
(faster)
1. First-tier(client)
handles only user interface
2. Second-tier(Application server)
handles business and data processing logic
3. Third-tier( Database server)
handles the database and the transaction logic