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Database Systems Concepts and Architectures ( CHAPTER 2 ) - Coggle Diagram
Database Systems Concepts and
Architectures ( CHAPTER 2 )
DATA MODEL
A collection of inter-related concepts that explains the data, relationship, and constraints on the data in a organization.
CATEGORIES
LOW LEVEL
( physical )
Describes how data is kept in the computer systems by representing record formats, order of records, and retrieval modes for data instances.
REPRESENTATION LEVEL
( implicational )
record-based data modelling.
the most common are relational hierarchy,
network models and object-oriented
models.
Database is represented with a record structure that consists of few fields from different data types and sizes.
HIGH LEVEL
( conceptual )
Uses concepts such as entities,
attributes and relationships
Also known as object-based
data modelling
ENTITIES
: real world objects, events / concepts stored in a database
example: EMPLOYEE (object), SPORT (event) / REGISTRATION (concept).
ATTRIBUTES
: characteristics that describe an entity
example: Employee’s name, employee’s number, address and telephone number.
RELATIONSHIP
: connects one or more entities in a database schema in line with the definition of database collection in inter-related data.
SCHEMAS AND INSTANCES
The description of the database is known as database scheme / meta-data.
Database scheme is determined during the design phase and seldom changed.
A database schema
: a collection of relations.
A relation schema
: a description of an object that is being modelled.
Instances
: a data in the database for that particular time.
DBMS ARCHITECTURE
LEVELS
CONCEPTUAL LEVEL
( The database views )
describes data and the relationship between data in the database
contains logical structure for the whole database viewed by the database administrator.
Users can build interfaces to access data in the database.
INTERNAL LEVEL
( how data is stored in the database )
look into physical implication and consideration
towards run-time performance and optimization
of storage space usage.
EXAMPLE:
Record description for storage
Record placement
Storage space allocation
for data and indices
Data compression and data
encryption techniques
EXTERNAL LEVEL
( User’s view of the database )
the relevant part of the database to a user.
each user can have different view of the database
the differences are because of different
application programs used + different access control.
DATA INDEPENDENCE
LOGICAL DATA INDEPENDENCE
Changes in conceptual schema do not
affect external schema.
users who are directly involved in the
changes need to update the programs
PHYSICAL DATA INDEPENDENCE
Changes in physical schema do not affect
external and conceptual schemas.
DATABASE LANGUAGES
DATA DEFINITION LANGUAGE ( DDL )
form a database schema that is to create,
update or delete a database schema.
DATA MANIPULATION LANGUAGE ( DML )
to access and update the existing
data in the database.
Common operations:
Insertion of a new data
Modification of an existing data
Deletion of unwanted data
Accessing data
TYPES OF DML
PROCEDURAL
identify what data is needed and how
the data can be accessed
exp: C++, C, COBOL, PASCAL
NON-PROCEDURAL
users only need to know what data needed to
be updated.
exp: SQL, QBE
DBMS
FUNCTIONS
enables users to store, retrieve
and update data in the database.
enable users to changes / accesses
the content of the database.
enable data in the database to
be updated correctly
Providing recovery services
Providing authorization services,
Providing support for data communication
Providing integrity services
enable users to know what data
has been stored in the database.
COMPONENTS
Database manager
File manager
Query processor
DML pre-processor
DDL compiler
Catalogue administrator
MULTI-USERS
File server
-Processing is distributed in the
network, usually local area
network.
Teleprocessing
one host computer with central
processing unit (CPU) connected
to a number of dumb terminals
with network cables.
Client-server
developed to solve problems in the previous architectures.