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Modelling Business Systems 6. Modelling and Managing Data. Elements of Data. Entity – something we hold information about Students, courses, customers, suppliers. Orders, accounts Concrete entities – e.g. student Abstract entities – e.g. accounts

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modelling business systems 6

Modelling Business Systems 6

Modelling and Managing Data

CB1004 Modelling Business Systems 6

elements of data
Elements of Data
  • Entity – something we hold information about
    • Students, courses, customers, suppliers. Orders, accounts
    • Concrete entities – e.g. student
    • Abstract entities – e.g. accounts
    • May not be components of the system e.g. suppliers but are part of the environment

CB1004 Modelling Business Systems 6

elements of data1
Elements of Data
  • Attributes – the actual information we hold
    • Student registration number, address, stock description, price of a stock item
      • Concrete – height of a cupboard
      • Abstract – price
  • Instances – occurrences of the entity
    • Student
  • Values – of attributes
    • Age = 18 or 24

CB1004 Modelling Business Systems 6

elements of data2
Elements of Data
  • Relationships – connection between entities
    • Each supplier has an account
  • Degree of relationship
    • One-to-one – a supplier has one account (unusual to have more than one, or not to have an account)
    • One-to-many – Arbor operations supply many customers
    • Many-to-many – a cupboard contains many parts, a particular part may go into more than one cupboard

CB1004 Modelling Business Systems 6

elements of data3
Elements of Data
  • Relationships cont.
    • Compulsory relationships – a supplier MUST have an account
    • Optional – not all academic staff work in CMS

CB1004 Modelling Business Systems 6

diagramming conventions
Diagramming Conventions

Account

Supplier

One-to-one

Operations

Customer

One-to-many

Parts

Cupboard

Many-to-many

CB1004 Modelling Business Systems 6

data models
Data models
  • Entity relationship diagram (ERD)
    • High level and abstract (conceptual)
    • Describes data in logical terms not its physical organisation
  • Draw one for Arbor #

CB1004 Modelling Business Systems 6

implementation models
Implementation models
  • Physical models
  • Hierarchical data model
    • Tree structure

CB1004 Modelling Business Systems 6

hierarchical tree data model
Hierarchical (tree) Data Model

Level 0

Level 1

Leaves

Level

2

Leaves

CB1004 Modelling Business Systems 6

hierarchical model
Hierarchical model
  • Child may have only one parent
    • Contradicts use of many-to-many relationships

CB1004 Modelling Business Systems 6

central assembly packing
Central assembly & packing

CAP

Employs

produces

Consists of

processes

Operator

Product

Production

facility

Used for

Carries out

Operation

CB1004 Modelling Business Systems 6

adjusting the model 2 parents
Adjusting the model – 2 parents

Operator

Production

facility

Operation

CB1004 Modelling Business Systems 6

replication
Replication

Operator

Production

facility

Operation

Operation

CB1004 Modelling Business Systems 6

pointers
Pointers

Operator

Production

facility

Operation

Pointer

CB1004 Modelling Business Systems 6

many to many
Many-to-many
  • Not solved by pointers
  • What connects various products to various production facilities is when any product is processed by a particular production facility
    • A production order or job - a logical entity

CB1004 Modelling Business Systems 6

many to many relationships
Many-to-many relationships

Production facility

Product

CB1004 Modelling Business Systems 6

replace by two one to many
Replace by two one-to-many

Production

facility

Product

Production

order

CB1004 Modelling Business Systems 6

arbor logical model
Arbor logical model
  • Need to replace the many-to-many relationships with one-to-many #

CB1004 Modelling Business Systems 6

hierarchical schema
Hierarchical schema

CB1004 Modelling Business Systems 6

hierarchical schema terminology
Hierarchical schema / terminology
  • How data is organised
  • Field- holds the value of a single attribute
  • Segment – group of fields
  • Sequence field – one of the fields within a segment used for ordering the segment
  • Analogies – filing cabinets, books with chapters etc

CB1004 Modelling Business Systems 6

network plex model
Network (plex) model
  • Concept of a set
    • Two entities with a one-to-many relationship
    • At one end is the owner, the other the member
    • Entities may belong to more than one set type as owners or members

CB1004 Modelling Business Systems 6

slide22

Central packing

Owner

Owner

Member

Member

Operator

Production

facility

Owner

Owner

Member

Member

Operation

CB1004 Modelling Business Systems 6

many to many relationships1
Many-to-many relationships
  • Instances
    • More than one operator
    • Each may carry out more than one operation
    • Can be resolved in a similar manner to the hierarchical database problem $
      • Introduce another (logical) entity e.g. production order

CB1004 Modelling Business Systems 6

slide24

Central packing

Owner

Owner

Member

Member

Production

facility

Product

Owner

Owner

Member

Member

Production

order

CB1004 Modelling Business Systems 6

terminology
Terminology
  • Data item – holds value of a single attribute
  • Vector – groups different values of the same attribute e.g. orderno
  • Repeating group – groups different types of values e.g. orderno and ordertype
  • Record – collection of data items, vectors or repeating groups
  • Key – data item used to select a record
  • Set – consists of an owner and members

CB1004 Modelling Business Systems 6

network schema
Network schema

Production order

Orderno

Prodno

Quantity

Process

Optype

Opno

1234

C126

150

1

Cutting

Grouting

2

CB1004 Modelling Business Systems 6

the problems
The problems
  • Both models based on the implementation of the database
  • Changes add to complexity

CB1004 Modelling Business Systems 6

relational model
Relational model
  • Based on a two dimensional flat table or flat file

CB1004 Modelling Business Systems 6

cupboards
Cupboards

CB1004 Modelling Business Systems 6

terminology1
Terminology
  • Columns – corresponds to an attribute of an entity
  • Rows – correspond to one instance of an entity
  • Relations – all the instances (the whole table)
  • Domain – a particular column of a relation
    • Set of attribute values

CB1004 Modelling Business Systems 6

the problems1
The problems $
  • Have several repeating groups
    • Calabria occurs many times - different sizes and finishes
  • Dependencies between domains
    • Stock class and siting
  • Could split to more than one table for different users
    • Style, model, finish, price – accounts
    • All except stock class – sales
      • Potential for duplication of data

CB1004 Modelling Business Systems 6

principles
Principles
  • Booch (1991)
    • The simplest yet most important goal in database design is the concept that each fact should be stored in exactly one place
      • Eliminates redundancy and potential storage requirements
      • Simplifies updating the database
      • Easier to prevent inconsistencies

CB1004 Modelling Business Systems 6

normalisation
Normalisation
  • Eliminates duplication where it is redundant
    • The value of ‘veneer’ is not dependent on the style ‘calabria’
      • Relationship between these two does not need separating
    • However, the siting and stock class always go together siting = lounge, stock class = LG
      • Needs to be looked at
    • Example #

CB1004 Modelling Business Systems 6

first normal form 1nf
First normal form (1NF)
  • Separates repeating groups
    • Cupboard example
      • First repeating group contains style
      • Second repeating group contains size
    • Note the necessity for multiple field keys as we break down the tables

CB1004 Modelling Business Systems 6

second normal form 2nf
Second normal form (2NF)
  • Removal of partial dependencies
    • In ‘Cupboard’
      • Values for height, fittings and price depend on style, size and surface finish
        • Value of price depends on variations in style, size and surface finish
        • Value of height only dependent on size – partial dependency
          • The value of a non-key attribute depends on the partial key NOT the whole key

CB1004 Modelling Business Systems 6

third normal form 3nf
Third normal form (3NF)
  • Removal of transitive dependencies – where the value of an attribute does not depend directly on the value of a key, but depends on the value of a second attribute which depends on the value of the key
    • ‘Application’
      • Value of stock class depends entirely on siting; siting depends on the key attributes of style and surface finish

CB1004 Modelling Business Systems 6

semantic data model sdm
Semantic data model (SDM)
  • Based on principles deriving from the user’s view of the meaning of the data
  • Entities correspond to objects in the ‘real world’
  • Classes are collections of entities that share the same set of attributes
    • Can also have subclasses

CB1004 Modelling Business Systems 6

slide38

Semantic model

CB1004 Modelling Business Systems 6

data processing and manipulation
Data Processing and Manipulation
  • Data definition language (DDL)
    • Defines structural features of the model
      • Create table, create view
  • Data manipulation language (DML)
    • Defines how data is accessed and manipulated
      • Insert, select
  • Data control language (DCL)
    • Controls access to the database and security
      • Grant, revoke, lock table

CB1004 Modelling Business Systems 6

dbms vs tradition
DBMS vs. tradition
  • Traditionally
    • Box file became a computer based file of sequential records
    • Direct access disk storage – led to less sequential storage of data
  • Now moving to a more logical view of data

CB1004 Modelling Business Systems 6

slide41
Cont.
  • Coffee machine #
    • First machine
      • Has columns of plastic cups already filled with ingredients
      • New requirement – physically add a new column of cups
    • Second machine
      • Makes up desired drink as requested
      • New requirements – change the logic in the machine to produce a new combination

CB1004 Modelling Business Systems 6

slide42
Cont.
  • DBMS utilises a similar system to the second machine
    • Brings together individual data items as the user requests them #

CB1004 Modelling Business Systems 6

the database
The database
  • Stored data
    • All the data required by the information system
    • In turn these are determined by the individual management systems e.g. financial system, personnel system etc
    • Same data may be used for different reasons e.g. sales figures
      • Report on the performance of a retail outlet
      • Analyse customer demand for future production targets

CB1004 Modelling Business Systems 6

the database cont
The database cont.
  • Meta data
    • Parts database for cupboards will contain data about the parts that make up a particular cupboard
    • Schema
      • Defines the ordering and arranging of this data in the data model
      • Enables us to understand the relationship of parts to one another

CB1004 Modelling Business Systems 6

as a result
As a result
  • The software used in databases is more user friendly and high level
    • Hence a detailed knowledge of computing is no longer necessary to create information systems
    • Build closer links between users and builders

CB1004 Modelling Business Systems 6

any questions
Any questions?

CB1004 Modelling Business Systems 6