COMP 6471 Software Design Methodologies

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COMP 6471Software Design Methodologies

• Winter 2006
• Dr Greg Butler
• http//www.cs.concordia.ca/gregb/home/comp647-w20
  06.html

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The CU WME Design Case Study

• Concordia University Work Management Environment
  (CU WME) provides support for an organisation of
  people who produce and publish documents
• Components
• User Management
• File Management
• Change Management
• Activity Management
• Collaborative Publication
• Project Management

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The CU WME Design Case Study

• How do components distribute responsibilities and
  what are their dependencies?
• Separate mechanisms from policy.
• Components
• User Management
• File Management
• Change Management
• Activity Management
• Collaborative Publication
• Project Management

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The CU WME Design Case Study

• How do components distribute responsibilities?
• User Management manage users, roles, rights
• File Management provide file/directories,
  operations for access, back-up. Access control?
• Change Management change of what?, provide
  operations, how much policy?
• Activity Management monitor, log. How much
  policy of control? What mechanisms for control?
• Collaborative PublicationDocument management
  mechanisms on documents, concept of document,
  what is difference between file mgmt vs doc mgmt?
• Project Management mechanisms for project
  definition, policy for .

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The CU WME Design Case Study

• What are their dependencies?
• User Management depends on FM?
• File Management depends on UM?
• Change Management depends on FM?
• Activity Management depends on FM, UM?
• Collaborative Publication depends on UM, FM, CM,
  AM
• Project Management depends on ???

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The CU WME Design Case Study

• Separate mechanisms from policy.
• Which set policy, which provide implementation to
  enforce policy, which provide basic mechanisms?
• Components
• User Management
• File Management
• Change Management
• Activity Management
• Collaborative Publication
• Project Management

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CU WME User Management

• Responsibility?
• RBAC (Role Based Access Control) concepts
• User
• Role (enumerated list)
• Operation (eg, read, write, )
• Object ( Resource, ie Document/File)
• Permission of Role to perform an Operation on
  Object
• RBAC1 allows role hierarchy (DAG)
• RBAC2 adds constraint condition (ie lock exists
  on Object) to modify permissions

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CU WME User Management

• Responsibility?
• Does not need to define specific roles for the
  system, not Operations, nor Objects these might
  be requirements from other Components.
• Eg, role of project management from PM (C6)
• Eg, operation read for Object file() from FM
  (C2)

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CU WME File Management

• Responsibility?
• Unix File System
• File is stream of bytes to provide uniform
  abstraction
• Directory hierarchy mixes files/directories/links
  as entries
• File identified by pathname (cf URI)
• Unix permissions (rwx) for roles (user, group,
  other)
• Does CUWME FM need its own access control?
• Who provides storage for UM?
• How to manage copies of files? Versions of files?

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CU WME File Management

• Responsibility?
• Back-up in FM
• What are mechanisms
• What are policies for back-up, where are they set
• What storage (ie files) are needed for back-up?
• Are these managed by FM?
• Do these have back-up needs?
• File replication in distributed system
• Same file exists in different location
• What does same mean here? Implications for file
  operations are
• How is this managed by FM?

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CU WME File Management

• Responsibility?
• Are files atomic?
• How does FM relate to Change Mgmt and Document
  Mgmt?
• Does FM set policy (ie define) how a document is
  stored by FM? How a change is stored in FM? How a
  change is named?
• Do we back-up files or documents? If both, how is
  doc back-up related to file back-up?
• Is a back-up a change, activity, copy, version,

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CU WME Change Management

• Responsibility?
• Concurrent Versions System (CVS)
• Is version control management system
• Versions of what? for CVS source code files,
  binaries, documentation
• Check-out/check-in to manage concurrent access
• Version branches which can be merged later
  (manually)
• Tracks versions, not changes
• Storing deltas (ie changes) is an implementation
  optimization

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CU WME Change Management

• Responsibility?
• Version of file or document or resource or ?
• Dependency on FM? for storage
• Which operations create a new version?
• Which do not?
• How do permissions on X carry over to permissions
  on version of X? or copy of X
• Who sets this policy? Where?

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CU WME Change Management

• Responsibility?
• Do change management of files
• This is basic building block.
• Do change management of documents
• Remember documents are composite/recursive.

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CU WME Activity Management

• Responsibility?
• Look at basic concepts of web session or DB
  transaction or Command pattern
• Session is a sequence of activities by a user
  (from beginning to end)
• Activity is execution of an operation (C1) or
  command (GOF) or activity (C6)
• AM (C4) records/logs activities with info
• Session, activity, user, role,
• Who is responsible for session creation?
• Collaborate with UM (C1) to ensure user has
  permission for the activity (operation).

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CU WME Activity Management

• Responsibility?
• Can a user have many sessions at once?
• Where are command objects created? Executed?
  Recorded?
• Does FM supply storage for log?
• How do operations which create versions
  communicate to CM (C3) that a version has been
  created?

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CU WME Activity Management

• Responsibility?
• Remember that AM provides mechanisms, not
  policies.

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CU WME Collaborative Publication

• Responsibility?
• is this just Document Management?
• It should provide mechanisms, not policy.
  However, it must provide mechanisms that support
  the enforcement of policy, eg concurrency.
• Does this component need to define specific roles
  and permissions? Or can this be done separately
  using UM (C1)?

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CU WME Collaborative Publication

• Responsibility?
• Think of a document as an XML document, ie
  composite.
• How do you capture dependencies between a
  document and its parts? And the files? And its
  build process? ie, compare document publication
  with software development
• You need back-up and versions of documents can
  you simply rely on FM back-up facility?

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CU WME Collaborative Publication

• Responsibility?
• I do not know of any good CP/DM(C5) system to
  refer you to as an example.
• groupware tends to focus on calendars, chat,
  notification rather than documents themselves.
• issue tracking tends to just look at issues and
  their resolution, but not document changes (or
  source code changes)
• OpenText Livelink is a Canadian example, but it
  does everything in CU WME and more
• Lotus Domino from IBM is also of interest

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CU WME Project Management

• Responsibility?
• Keep the scope simple.
• This is the place for policy maybe not the only
  place.
• Define project
• Sequence of activities, resources (ie roles)
  required, and schedule (in timeunits of
  duration).
• Create project
• Set start date, assign users to roles.
• Monitor project progress
• Collaborate with UM (C1) so that user session is
  associated with a project and role assigned
  activities are RBAC operations on certain
  objects.
• Collaborate with AM (C4) to check whether
  activities are done.

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CU WME Project Management

• Responsibility?
• Composite pattern for project? Or for process?
• So a project can be a sequence of activities
  and/or subprojects. Allows easier definition of
  projects.
• Set/enforce policy? User can only work on
  assigned projects? User can only do scheduled
  activities?

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CU WME Project Management

• Responsibility?
• Again, difficult to find a simple example for
  you.
• Java open source projects include Ganttproject
  (a MS Project in Java) and teamwork.
• OpenText Livelink has project management.

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Fig. 13.3
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Important Concepts

• Model
• Abstraction hiding (unimportant) details
• Eg, cover of Larmans book
• GRASP Principle
• for assigning responsibility
• Design pattern
• Solution to design problem in context
• Eg, Command pattern

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Responsibility-Driven Design (RDD)

• Detailed object design is usually done from the
  point of view of the metaphor of
• Objects have responsibilities
• Objects collaborate
• Responsibilities are an abstraction.
• The responsibility for persistence.
• Large-grained responsibility.
• The responsibility for the sales tax calculation.
• More fine-grained responsibility.

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The 9 GRASP Principles

1. Creator
2. Expert
3. Controller
4. Low Coupling
5. High Cohesion
6. Polymorphism
7. Pure Fabrication
8. Indirection
9. Protected Variations

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Command Pattern

• You have commands that need to be
• executed,
• undone, or
• queued
• Command design pattern separates
• Receiver from Invoker from Commands
• All commands derive from Command and implement
  do(), undo(), and redo()
• Also allows recording history, replay