Download MIS515.6b

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Designing Databases
A database is an integrated collection of stored data
that is centrally managed and controlled.
Database management system is a systems software
that manages and controls access to a database.
A database consists of two related stores of infomation;
1.Physical data store : The storage area used by a
database management system to store the raw bits and
bytes of a database
2.Schema : Contains additional information about the
data stored in the physical data store including;
1.
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3.
Access and content controls
Relationships among data elements and groups of data
elements
Details of physical data store organization
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Designing Databases
A DBMS has four key components;
1.
An application program interface (API)
2.
A query interface
3.
An administrative interface
4.
An underlying set of data access programs and
subroutines
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Database Models
DBMSs have evolved through a number of stages since
their introduction. The most significant change has been
the type of model used to represent and access the
content of the physical data store. Four such model
types have been widely used;
1.Hierarchical
2.Network
3.Relational *
4.Object-oriented *
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Database Models
•Hierarchical : Represents data using sets of records
organized into a hierarchy
•Network :Groups data elements into sets of records
but allows those records to be organized into more
flexible network structures
•Relational : Stores data in tables
•Object-oriented : Stores data as objects or class
instances
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Relational Model
A relational database management system (RDBMS) is
a DBMS that stores data in tables .
Table : A two-dimensional data sturucture containing
rows and columns; also called a relation
Row : The portion of a table containing data that
describe one netity, relationship, or objcet; also called a
tuple or record
Field : A column of a relational database table; also
called an attribute
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Relational Model
Field Value : The data value stored in a single cell of a
relational database table; also called an attribute value
or data element
Key : A field that contains a value that is unique within
each row of a relational database table
Primary Key : A key used to uniquely identify a row of
a relational database table
Foreign Key : A field value stored in one relational
database table that also exits as a primary key value, in
another relational database table
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Relational Model
Designing Relational Databases
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Create table for each entity
2.
Choose a primary key for ecah table (invent one, if
necessary)
3.
Add foreign keys to represent one-to-many
relationships
4.
Create new tables to represent many-to-many
relationships
5.
Define referential integrity constraints
(a consistent relational database state in which
every foreign key value also exists as a primary
key value)
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Relational Model
Designing Relational Databases
6.
Evaluate schema quality and make necessary
improvements
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Uniqueness of table rows and primary keys
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Lack of redundant data
Normalization : A process that ensures relational
database schema quality by minimizing data
redundancy
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7.
Ease of implementing future data model
changes
Choose appropriate data types and value
restrictions (if necessary) for each field
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Object-Oriented Model
An object database management system (ODBMS) is a
DBMS that stores data as objects or class instances
Object Definition Language (ODL) is a standard object
database descripion language for describing the
structure and content of an object database.
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Object-Oriented Model
Designing Object Databases
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Determine which classes require persistent storage
2.
Define persistent classes
3.
Represent relationships among persistent classes
4.
Choose appropriate data types and value
restrictions (if necessary) for each field
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Object-Oriented Model
Representing Classes
Objects can be classified into two broad types for
purposes of data management;
Transient object : An object that doesn’t need to store
any attribute values between instantiations or method
invocations
Persistent object : An object that must store one or
more attribute values between instantiations or method
invocations
An object database schema includes a definition for
each class that requires persistent storage. ODL class
definitions can derive from the corresponding UML
class diagram.
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Object-Oriented Model
Representing Relationships
Each object stored within an ODBMS is automatically
assigned a unique object identifier.
Object identifers are used to relate objects of one class to
objects of another class.
An ODBMS represents relationships by storing the identifier
of one object within related objects.
The ODBMS uses attributes containing object identifiers to
find objects that are realted to other objects. The process of
extracting an object identifier from one object and using it to
access another object is called navigation.
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Object-Oriented Model
Representing Relationships
The keyword relationship is used to declare a relationship
between one class and another. (one-to-one, one-to-many,
many-to-many)
An association class is a class that represents a relationship
and stores the attributes of that relationship.
Generalization relationships show a generalization hierarchy
from the class diagram.
Key attributes are not required in an object database since
referential integrity is implemented with object identifiers,
however they are useful in guaranteeing unique object
content and providing a means of querying database
contents.
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Hybrid Object-Relational Model
Hybrid object-relational model is a relational database
management system used to store object attributes and
relationships. It is also called hybrid DBMS and mixes
elements of both the relational and OO approaches.
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