INFO1408 Database Design Concepts Week 6 Database Components

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INFO1408 Database Design ConceptsWeek
6Database Components

• Two basic concepts to explore
• Conceptual Design Components
• Logical/Physical Design Components

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(words that appear in blue are missing from your
notes .. You need to write them in to ensure you
have a complete record of this session)
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Conceptual Design

• Technology independent
• can be implemented on any database
• An activity carried out by a data-modeler

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Logical Design

• Process of translating (mapping) the conceptual
  design to fit the chosen database model
  (relational, object oriented etc.)
• An activity carried out by a
• database designer

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Physical Design

• Mapping the logical design to one or more
  physical designs
• Tailored to the particular DBMS being used and
  the computer system on which the database will
  run.
• An activity usually performed by a Database
  Administrator (DBA)

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Entities

• Something of interest to the activity we are
  trying to model
• Could be a person, place, thing, concept about
  which data is collected
• Just about anything that can be named with a noun
  can be an entity we should restrict ourselves to
  things of interest to the users of our database.

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• A very common entity that is found in many
  business oriented databases is the
• Conceptually this represents all the customers in
  the database an individual customer is known
  as an instance of the entity

CUSTOMER
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Attributes

• An attribute is a unit fact that characterises
  or describes an entity in some way
• Attributes can not be broken down into smaller
  units in any meaningful way they are the
  smallest unit of information that is stored
  within the database
• A particularly important attribute is the unique
  identifier for the entity

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An entity is composed of attributesan example
the customer entity can be represented as .
CUSTOMER
Entity
attributes
Unique identifier
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Relationships

• Relationships are the associations among entities
• Relationships are represented at the conceptual
  level by lines joining entities together.
• Each end of the relationship line shows the
  maximum cardinality of the relationship (maximum
  number of instances of one entity that can be
  associated with the entity at the other end of
  the relationship line)

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Entity-Relationship modelling

• It is important to realise that there are a
  number of different ways of representing the
  details of relationships and cardinality
• For the purposes of this module we want to
  explore the underpinning concepts involved at
  this we will use the notational style used in the
  text book . You will come across different
  styles as your experience of data modelling
  develops through your course

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You need to be confident that you understand

• One-to-One relationships
• One-to-Many relationships
• Many-to Many relationships
• Read Pages 28 to 32 of
• Databases Demystified
• until you have this confidence

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Business Rules

• Very important a policy, procedure or standard
  that an organisation has adopted.
• These business practices must be reflected in the
  construction and functioning of the database
• They may impose constraints on the database design

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Logical Physical (1)Tables

• Primary unit of storage in the relational model
  is the table
• A two dimensional structure composed of rows and
  columns
• Each row represents one occurrence (instance) of
  the entity
• Each column represents one attribute for that
  entity.

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Columns and Data types

• The data type specifies the category for the
  format of the data represented in a tables
  column. Common data types are
• TEXT
• NUMBER
• DATE/TIME
• CURENCY

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Constraints

• Primary Key Constraints
• Focus around the non duplication of unique
  identifiers for entities within the database.
• Referential Integrity Constraints
• Focus particularly around the implications of
  adding new data to, or deleting data from, the
  database

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Views

• A stored database query that provides the user
  with a customised subset of the data from one or
  more tables
• Can be thought of as a virtual table