1. UC San Diego CSE 294 May 7, 2010 Barry Demchak
Requirements Engineering From System Goals to UML Models to Software Specifications Axel van Lamsweerde Universite catholique de Louvain, BE
Hagia Sophia – AD 558
UC San Diego
CSE 294
May 7, 2010
Barry Demchak

2. Dreaming of an Online Bookstore
Multiple Orders
Pricing, Payment,
Accounts
How do I:
Discover the requirements?
Translate them into a design?
Know that the design is complete?
Change the requirements?
Update the design?
Order
Fulfill
Deliver
Deliver
Stocks
Couriers
Address, Retry, Rejection, Return

3. Goal-Oriented Model Building
Build Preliminary Goal Model (w/ scenarios)
Derive Object Model
Update Goal Model (w/ new goals)
Derive Updated Object Model
Analyze obstacles, threats, conflicts
Build agent model (w/ responsibilities)

4. Goal-oriented RE Use goals for Requirements elicitation Evaluation
Negotiation
Elaboration
Structuring
Documentation
Analysis
Evolution

5. Agenda Goal orientation in a MDE/MDA world Goal formulation
Object modeling basics
Representing goals with object models
Further possibilities

6. Table of Contents Fundamentals of Requirements Engineering
Setting the Scene
Domain Understanding and Requirements Elicitation
Requirements Evaluation
Requirements Specification and Documentation
Requirements Quality Assurance
Requirements Evolution
Goal Orientation in Requirements Engineering (ch 7)
Building System Models for Requirements Engineering
Modeling System Objectives with Goal Diagrams
Anticipating What Could Go Wrong: Risk Analysis on Goal Models
Modeling Conceptual Objects with Class Diagrams (ch 10)
Modeling System Agents and Responsibilities
Modeling System Operations
Modeling System Behaviors
Integrating Multiple System Views
A Goal-Oriented Model-Building Method in Action (ch 15)
Reasoning about System Models
Semi-Formal Reasoning for Model Analysis and Exploitation
Formal Specification of System Models
Formal Reasoning for Specification Construction and Analysis

7. Review Model Driven Engineering (MDE) Model Driven Architecture (MDA)
Rich Services, MDE, MDA, and RE

8. Model Driven Engineering
Produces models tailored to important points of view
Resource management, security, etc
Structural vs dynamic
Models represent abstractions at coarse, medium, and fine granularities
Models expressed in common language (e.g., UML)
Relies on tools and processes for
Maintaining models
Transforming one model to another
Demonstrating important properties of models

9. Model Driven Architecture
Platform Independent Model
Computation Independent Model
Platform Specific Model
Today
Approach that can produce SOAs
Fidelity of alignment between user requirements and application
Multilevel modeling (…UML)
Transformations between models … bidirectional
NO GAPS
Complimentary to SOA
Roles
Interactions
Separation of logical and deployment models
Supports hierarchical development

10. Rich Services CIM/PIM Process
Agility
Completeness
Scalability
End-to-End
Alignment
No Gaps

11. Goal-Oriented Model Building
Build Preliminary Goal Model (w/ scenarios)
Derive Object Model
Update Goal Model (w/ new goals)
Derive Updated Object Model
Analyze obstacles, threats, conflicts
Build agent model (w/ responsibilities)

12. Goals, Agents, and Entities come from scenarios
Definitions
Goal
Prescriptive statement of intent
System (to-be or as-is) satisfies via cooperation of agents in manipulating entities
Agent
An active component that manipulates entities
Entity
A passive component containing state
Goals, Agents, and Entities come from scenarios

13. Benefits of Goals (Preview)
Goal refinement leads to structuring complex abstractions at multiple levels
Rationale (and traceability) for requirements
Rich structure for “satisfaction arguments”
Aligns system with customer’s strategic need
Allows demonstration of completeness and pertinence
Provide anchors for risk analysis
… and 6 other benefits, too!

14. Goal Examples Well-formed goals Non-goals
The store shall deliver each book the shopper orders.
Each book shall have a price specific to the shopper.
The shopper shall be charged for any book delivered.
Non-goals
To order a book, the shopper browses a catalog, chooses a book, and submits an order. The shopper can pay COD or Paypal.
The system shall guarantee delivery of each book.
The first non-goal is a use case, and goals can be derived from it
The second non-goal identifies an actor out of the scope of known actors
Agent
Entity

15. About Goals (& Statements)
Granularity
High level goals are strategic (#1)
Low-level goals are decompositions identifying technical objectives – involve fewer actors
Requirement
A goal under responsibility of single agent (#3)
Enforceable by the application
Expectation
Like a requirement
Cannot be enforced by the application
e.g., The shopper will order 3 books a week
#1: The store shall deliver each book the shopper orders.
#3: The shopper shall be charged for any book delivered.

16. More About Goals & Statements
Assumption
Factual information subject to change
e.g., Books can be delivered Monday-Saturday
Domain Property
Invariant descriptive property about environment
e.g., An order can be filled iff it contains books

17. Goal Behaviors Meta-goal
Agent behaviors satisfy goals by sequencing state transitions
Application behavior is closure of all agent behaviors
 Application SATISFIES GOALS
Achieve
if CurrentCondition then sooner-or-later TargetCondition
e.g., if a book is ordered, it is shipped within 24 hours
Maintain
always if SomeCondition then GoodCondition
e.g., always if a book is in stock, it is listed in the catalog
Soft
Prescribe preferences among behaviors (e.g., responsive UI)
Behavioral goal
Agent behavior: sequence of state transitions the agent controls
System behavior: Closure of agent behaviors
We want GOAL SATISFACTION

18. Goal Categories

19. Using Goal Categories Eliciting missing goals Detecting goal conflicts
e.g., Is there a security goal for order placement?
Detecting goal conflicts
e.g. Is there a conflict between usability and security?
Conflict resolution
e.g., Security goals have the highest priority
Specifying goals
e.g., Confidentiality are Avoid goals about knowledge that agents may have about each other

20. Candidate Goals for Bookstore
A shopper purchases books from the store
Store offers catalog of books
Shopper orders one or more books from catalog
Shopper specifies payment
Shopper gives credit card OR
Shopper gives Paypal OR
Shopper references shopper account
Shopper specifies shipping
Shopper gives shipping address OR
Order is shipped via courier

21. Graphical Goal Representation
A. van Lamsweerde. Requirements Engineering. John Wiley & Sons Ltd. West Sussex, England

22. Goal-Oriented Model Building
Build Preliminary Goal Model (w/ scenarios)
Derive Object Model
Update Goal Model (w/ new goals)
Derive Updated Object Model
Analyze obstacles, threats, conflicts
Build agent model (w/ responsibilities)

23. KAOS – the Object Model
Keep
All
Objectives
Satisfied

24. Modeling – Conceptual Objects
Entity
Autonomous and passive containers of state (e.g., book)
Association
Dependent on objects (called roles) it links (e.g., book-catalog)
Agent
Autonomous and active – has behavior, and changes states (e.g., shopper)
Event
Instantaneous existence based on system state (e.g., buy book)

25. Entity Features as Model Notations
Name
Book
Type
Entity
Def
A bound edition
Has
Title, Author, Publisher, Date
DomInvar
Book is valid iff Title, Author, Publisher, Date all not null
Init
Set all null

26. Agent Features as Model Notations
Name
Shopper
Type
Agent
Def
Any person having an account
Name
Buy
Type
Association
Def
Relationship between buyer and item purchased
DomInvar
Item is valid and Purchaser has funds

27. Arity of Associations 4-way association
Goals: Shopper can choose a book and designate a bank. The shipper will ship the book to the shopper.
4-way association

28. Goal → Object Model Heuristics
Overall objective: complete, pertinent, traceable models
Model only objects and properties referenced in goals
Create associations from word patterns like <source> <linkverb> <target>, etc.
Identify generalizations where objects have similar attributes, associations, or invariants
Model pointers as associations
Don’t pollute models with links that belong in other models
… 5 more in the text

29. A Candidate Model

30. Goal-Oriented Model Building
Build Preliminary Goal Model (w/ scenarios)
Derive Object Model
Update Goal Model (w/ new goals)
Derive Updated Object Model
Analyze obstacles, threats, conflicts
Build agent model (w/ responsibilities)
Tomorrow is another day

31. Future Presentations Analyzing obstacles, threats, and conflicts
Modeling agents and responsibilities
Modeling system operations
Merging object, agent, and system views
Semi-formal reasoning
Formal reasoning

32. Research Opportunities
Tools
Organize and categorize goals
Generate goal gap questions
Parse goals and generate models
Maintain traceability between goals and model
… more … ?

33. Questions