Domain Model Visualizing Concepts

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Domain Model Visualizing Concepts

• Chapter 9
• Applying UML and Patterns
• Craig Larman

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Comments on diagrams

• Now that we are starting to look at diagrams, I
  want to emphasize that this is a class on
  analysis and design, not diagramming. While it
  may look good on your resume that you can use
  UML, your career depends on being able to
  translate ideas into good systems. That is much
  more difficult.

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Domain Model Relationships
Domain Model
Business Model
Classes, attributes, associations
Elaboration on some terms
Domain objects
Use Case Model
Glossary
Requirements
Interaction Diagrams
Design
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A Domain Model

• illustrates meaningful conceptual classes in a
  problem domain.
• is a representation of real-world concepts, not
  software components.
• is NOT a set of diagrams describing software
  classes, or software objects and their
  responsibilities.

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A Domain Model is the most important OO artifact

• Its development entails identifying a rich set of
  conceptual classes, and is at the heart of object
  oriented analysis.
• It is a visual representation of the
  decomposition of a domain into individual
  conceptual classes or objects.
• It is a visual dictionary of noteworthy
  abstractions.

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Domain Model UML Notation

• Illustrated using a set of class diagrams for
  which no operations are defined.
• It may contain
• Domain Objects or Conceptual Classes
• Associations between conceptual classes
• Attributes of conceptual classes

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A Domain Model is not a Software Artifact
Software Artifacts

• A Conceptual class

SalesDatabase

Sale
Date Time
vs.
Sale
Date Time
Print()
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Think of Conceptual Classesin terms of

• Symbols words or images
• Intensions its definition
• Extensions the set of examples to which it
  applies
• Symbols and Intensions are the practical
  considerations when creating a domain model.

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Decomposition

• A central distinction between Object-oriented
  analysis and structured analysis is the division
  by objects rather than by functions during
  decomposition.
• During each iteration, only objects in current
  scenarios are considered for addition to the
  domain model.

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Conceptual Class Identification

• It is better to overspecify a domain with lots of
  fine-grained conceptual classes than it is to
  underspecify it.
• Discover classes up front rather than later.
• Unlike data modeling, it is valid to include
  concepts for which there are no attributes, or
  which have a purely behavioral role rather than
  an informational role.

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Identify Conceptual Classesby Category List

• Common Candidates for classes include
• Tangible objects, Descriptions, Roles,
• Places, Transactions, Containers,
• Systems, Abstract nouns, Rules,
• Organizations, Events, Processes,
• Written Materials, Catalogs, Records,
• Financial Instruments and Services

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Identify Conceptual Classesby Noun Phrase

• Identify Nouns and Noun Phrases in textual
  descriptions of the domain.
• Fully dressed Use Cases are good for this type of
  linguistic analysis.
• Its not strictly a mechanical process
• Words may be ambiguous
• Different phrases may represent the same concepts.

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Sales Domain example - Purchase Items Use Case

• We find concepts such as Register, Sale, Item,
  Customer, Receipt etc. in this use case.
• Should we include Receipt in the Model?
• Con As a report of a sale, its duplicate info.
• Pro Business Rules for a Return require that the
  customer has a receipt.
• Suggestion Include it in the iteration where the
  Return Use Case is covered.

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Steps to create a Domain Model

• Identify Candidate Conceptual classes
• Draw them in a Domain Model
• Add associations necessary to record the
  relationships that must be retained
• Add attributes necessary for information to be
  preserved
• Apply existing Analysis Patterns

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Apply the Mapmaker Strategy

• Use existing names for things, the vocabulary of
  the domain
• Exclude irrelevant features
• Do not add things that are not there

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A Common Mistake - Classes as Attributes

• Rule If we do not think of a thing as a number
  or text in the real world, then it is probably a
  conceptual class.
• If it takes up space, then it is likely a
  conceptual class.
• Examples
• A Store is not an attribute of a Sale
• A Destination is not an attribute of a flight

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Specification or Description Conceptual Classes

• A Class that records information about an item.
• Even if all Instances of the item are sold out,
  the description remains.
• Avoids duplication of recording the descriptive
  information with each instance of the item.

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Description of a Service Example (Flight)
Flight
Date Time Number
Airport
Name
Flies-to
vs.
Flight
Date Time
FlightDesc
Date Time
Airport
Name
Described -by
Describes -flights-to
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Monopoly Concepts (candidates)
Monopoly Game
Player
Piece
Square
Die
Board
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UML Notation Multiple Perspectives

• UML describes raw diagram types, such as class
  diagrams. It does not impose a specific method or
  process.
• UP, the Unified Process, applies raw UML to
  defined methodology models.
• UML can be used for 3 different perspectives
• Essential describe the real world
• Specifications software abstractions, such as
  components and their interfaces
• Implementation specific language (Java)