The Shlaer Mellor Object Orientated Methodology

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The Shlaer Mellor Object Orientated Methodology

• By

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Background

• Sally Shlaer
• Stephen L. Mellor
• Produced the Shlaer-Mellor Method through
  experience gained while developing computer
  systems in the 1980s
• It is designed to aid engineers in modelling the
  requirements of the system using a formal and
  structured manor

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Working outside your area of expertise

• A programmer is generally not an expert in the
  proposed system
• To implement efficiently, a programmer must
  become an expert in the real-time system

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Solution

• Firstly, identify the objects involved within the
  system
• An object is an abstraction of a real world
  thing
• Class of PASSENGER AIRCRAFT
• Used to make instances of PASSENGER AIRCRAFT

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Solution Cont.

• Identify the attributes
• An attribute is a abstraction of a
  characteristic possessed by all instances of an
  object
• Shlaer, Mellor (1988) Object-Oriented Systems
  Analysis Modeling the World in Data Yourdon
  Press

Aircraft Aircraft ID Name No. of
Passengers Speed
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Solution Example Objects

• Aircraft
• Aircraft ID
• Pilot ID (R)
• Name
• No. of Passengers
• Speed

Pilot Pilot ID Name Licence No
Is flown by

• This will help to structure the learning process
  for the programmer by identify the areas that
  need to be understood

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Multiple Vocabularies

• Discrepancies within vocabulary definitions
  between project teams.
• an order in the Shipping Department is quite
  different from an order in sales
• Shlaer, Mellor (1988) Object-Oriented Systems
  Analysis Modeling the World in Data Yourdon
  Press

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Solution

• The Shlaer Mellor method controls this
  misinterpretation by producing an Object
  Specification Document.
• This is produced using three sets of stringent
  rules including
• Description Guidelines
• Domains
• Naming conventions

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Solution Object Descriptions

• Object description is a short informative
  statement describing the objects role, this must
  include
• Inclusion Criteria
• Exclusion Criteria
• Context of Object
• Background Information.

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Solution - Domains

• A domain is the restriction on an attribute and
  must conform to one of the following
• enumeration domain
• citation domain
• acceptance rule
• range domain
• Same As domain

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Solution Naming Conventions

• The naming of objects within the model should
  remain constant with the real world objects.
  These must conform to one of the following
• Common names
• Strong names
• Precise names
• Names base on essential nature

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Changing information

• All instances of dynamic objects must be
  accommodated for.
• this pattern of change is a reality that needs
  to be accommodated in our software development
  process
• Shlaer, Mellor (1988) Object-Oriented Systems
  Analysis Modeling the World in Data Yourdon
  Press

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Solution Modelling Relationships

• Shlaer-Mellor method deals with this by using the
  following relationships.
• There are three main types of relationships
• One-to-One (11)

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Solution Modelling Relationships

• One-to-Many (1M)
• Many-to-Many (MM)

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Solution Correlation
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Solution - Conditional Relationships

• Not all instances have to partake in the
  relationship

a
b
a
a
b
a
b
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Solution Supertypes Subtypes

• Aircraft
• Aircraft ID
• Name
• No. of Passengers
• Speed

is a
Helicopter Helicopter ID Rotor
Diameter Vertical Lift
Jet Fighter Jet Fighter ID Armament Ejector
seat model
Jumbo Jet Jumbo Jet ID Luggage Toilets
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Uncertainty

• The lack of understanding of system elements that
  you are expected to know.
• If a programmer is uncertain about aspect of the
  system, they wont ask for clarification in-case
  he/she is expected to know this information.

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Solution Object Testing

• By testing the object there should be no
  uncertainty in the description of the objects or
  attributes. This method has been successful
• Team Members also found that the OOA models made
  it easier to communicate with the various
  developers and within other groups and users of
  the system
• Use In the Real World online Available
• (www.nrt.se/nrt/uml/WhitePapers/UsedInTheRealWorld
  .pdf) 1999

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Solution - Object Testing

• Object Testing includes
• Uniformity test
• More-than-a-name test
• The OR test
• More-than-a-list test

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Solution Attribute Testing

• Attribute testing is broken down into three
  procedurals.
• First rule One instance of an object has one
  value for each attribute
• Second rule Attributes must contain no
  internal structure
• Third rule Each attribute that is not part of
  an identifier must represent a characteristic of
  the instance named by the identifier and not a
  characteristic of some other non-identifier
  attribute

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Faulty Expert Knowledge

• This problem occurs when all the information on
  the real-time system is collected from one source
  
• The identifying and testing of the objects in the
  Object Specification Document and Information
  Structure Diagram ensures that this will not
  happen

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Solution - Information Structure Diagram

• Order
• Order ID
• Date
• Delivery Date
• Dispatch Date
• Total

Product Product ID Name Price
Customer Customer ID Name Address Payment
Details
Aircraft Aircraft ID Name No. of
Passengers Speed
Trade Customer TC ID Licence VATcode
Retail Customer RC ID Loyalty Points
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Shlaer Mellor Method

• Thank-You for listening
• If there are any questions please ask them now.