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Chapter 5, Requirements Analysis (2/2)

Chapter 5, Requirements Analysis (2/2). Analysis Object Model: Identifying Participating Objects. Pick a use case and look at its flow of events Find terms that developers or users need to clarify in order to understand the flow of events Look for recurring nouns (e.g., Incident),

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Chapter 5, Requirements Analysis (2/2)

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  1. Chapter 5, Requirements Analysis (2/2)

  2. Analysis Object Model:Identifying Participating Objects • Pick a use case and look at its flow of events • Find terms that developers or users need to clarify in order to understand the flow of events • Look for recurring nouns (e.g., Incident), • Identify real world entities that the system needs to keep track of (e.g., FieldOfficer, Dispatcher, Resource), • Identify real world procedures that the system needs to keep track of (e.g., EmergencyOperationsPlan), • Identify data sources or sinks (e.g., Printer) • Be prepared that some objects are still missing and need to be found: • Model the flow of events with a sequence diagram • Always use the user’s terms

  3. Analysis Object Model:Example – Analyzing The Flow of events (1/2) • Flow of events • The customer enters the store to buy a toy • It has to be a toy that his daughter likes and it must cost less than 50 Euro. • An assistant helps him. • The suitability of the toy depends on the age of the child. • His daughter is 8 years old • The assistant recommends a type of toy, namely the board game “Monopoly“ • Not a good description, but okay as an example

  4. Analysis Object Model:Example – Analyzing with Abbott’s (2/2) Example Grammatical construct UML Component “Monopoly" Proper noun Object “toy“, “board game” Common noun class "8 years old" Adjective Attribute “enters" verb Method “depends on…." Intransitive verb Method “is a" ,“either..or", “type of…" Classifying verb Inheritance "Has a ", “consists of" Having Verb Aggregation “must be", “less than…" modal Verb Constraint

  5. Analysis Object Model:Three Object Types • Entity Objects • Represent the persistent information tracked by the system (Application domain objects, “Business objects”) • Boundary Objects • Represent the interaction between the user and the system • Control Objects • Represent the control tasks performed by the system • Having three types of objects leads to models that are more resilient to change • The interface of a system changes more likely than the control • The control of the system change more likely than the application domain

  6. Analysis Object Model: Example - Breakout Game Display GameControl Points LeftButton HighScore RightButton GameState Boundary Objects Control Objects Entity Objects

  7. Analysis Object Model: Example - Breakout Game (Naming in UML) • UML provides several mechanisms to extend the language • UML provides the stereotype mechanism to present new modeling elements <<Boundary>> Points <<Entity>> Display <<Control>> GameControl <<Entity>> LeftButton <<Boundary>> HighScore <<Entity>> RightButton <<Boundary>> GameState

  8. Identifying Key Objects:Entity Objects • Represents persistent or long-lived information tracked by the system • Real-World entities (FieldOfficer) • Real-World activities (EmergencyOperationsPlan) • Recurring Nouns that are used in the UCs • Data Sources or Sinks Represent the persistent information tracked by the system (Application domain objects, “Business objects”)

  9. Identifying Key Objects:Boundary Objects • Represent the system interface for the actors • Forms, Messages, Terminals for different users • Identify Forms the user needs to enter data into the system • Identify messages the system uses to respond to the user • Identify terminals (computers) that are given to each actor • Described in End User Terms • Good: EmergencyReportForm, ReportButton • Bad: MenuItem, ScrollBar (too detailed) • Represent the interaction between the user and the system

  10. Identifying Key Objects:Control Objects • Responsible for coordinating boundary and entity objects • Collecting information from boundary objects • Dispatching it to entity objects • Control of distributed systems • One Control Object per Use Case (no counterpart in real world) • Life span covers the extent of a use case (user session) • Represent the control tasks performed by the system

  11. CancelButton ZoneButton Button Identify dependencies:Generalization and specialization • Inheritance as the guiding concept • Generalization • Abstract activity or concept out of low-level ones • Specialization • Start with the general case + refinement

  12. Identify dependencies:Associations and Aggregates • An Association consists of • Name • Roles (2 or more) • Multiplicity • Can be derived from UC (verbs), i.e. „man has two children“ • Important for entity objects • Important information of the application domain (compare with ER-Model in the database world) • Look out for Aggregations • Note the difference between • Composition (Lifetime is dependent) • (Shared) aggregation

  13. Steps to Analysis (1/3) • Formulate a few scenarios with the help from the end user and/or application domain expert • Extract the use cases from the scenarios, with the help of application domain expert • Analyze the flow of events, i.e. with Abbot's textual analysis • Generate the class diagrams, which includes the following steps: • Class identification (textual analysis, domain experts). • Identification of attributes and operations (sometimes before the classes are found!) • Identification of associations between classes • Identification of multiplicities • Identification of roles • Identification of constraints

  14. Steps to Analysis – Management (2/3) • Explicitly schedule meetings for object identification • First just find objects • Then try to differentiate them between entity, interface and control objects • Find associations and their multiplicity • Unusual multiplicities usually lead to new objects or categories • Identify Inheritance: Look for a Taxonomy, Categorize • Identify Aggregation • Allow time for brainstorming • Iterate, iterate, iterate …

  15. Steps to Analysis – Problems (3/3) • Missing domain know how • Missing technical knowledge • Disagreements between developers and users • Important decisions are deferred

  16. Dynamic Modeling • Definition of dynamic model • A collection of multiple state chart diagrams, one state chart diagram for each class with important dynamic behavior. • Purpose: • Detect and supply methods for the object model • How do we do this? • Start with use case or scenario • Model interaction between objects  sequence diagram • Model dynamic behavior of a single object  state chart diagram Entity objects normally must not have any dynamic behavior

  17. Dynamic Modeling with UML • Sequence Diagram • Can be read out of use cases • Dynamic behavior of a set of objects arranged in time sequence • Good for real-time specifications and complex scenarios • Information of the life time of objects • Relationships between objects (need for interfaces) • State Chart Diagram • describes the dynamic behavior of a single object • A state machine that describes the response of an object of a given class to the receipt of outside stimuli (Events).

  18. Dynamic Modeling with CRC(Classes, Responsibilities, Collaborators) • Tracking tool [Beck and Cunningham 1989] • Card Game • One Card represents one class (CoinControl) • Describe the resonsibities of that class (checkInsertedCoin) • Describe the needed classes(CoinDescription) • Can be used for discussing design ClassName Responsibities... Needed Classes...

  19. Dynamic Modeling of User Interfaces • Statechart diagrams can be used for the design of user interfaces • Also called Navigation Path • States: Name of screens • Graphical layout of the screens associated with the states helps when presenting the dynamic model of a user interface • Activities/actions are shown as bullets under screen name • Often only the exit action is shown • State transitions: Result of exit action • Button click • Menu selection • Cursor movements • Good for web-based user interface design

  20. Practical Tips for Dynamic Modeling • Construct dynamic models only for classes with significant dynamic behavior • Consider only relevant attributes • Use abstraction if necessary • Look at the granularity of the application when deciding on actions and activities • Reduce notational clutter • Try to put actions into state boxes (look for identical actions on events leading to the same state)

  21. Functional Modeling Object Modeling Dynamic Modeling Summary: Requirements Analysis • What are the transformations? • Create scenarios and use case diagrams • Talk to client, observe, get historical records, do thought experiments • What is the structure of the system? Create class diagrams • Identify objects. • What are the associations between them? What is their multiplicity? • What are the attributes of the objects? • What operations are defined on the objects? • What is its behavior? • Create sequence diagrams • Identify senders and receivers • Show sequence of events exchanged between objects. Identify event dependencies and event concurrency. • Create state diagrams • Only for the dynamically interesting objects.

  22. Requirements Analysis Document Template 1. Introduction 2. Current system 3. Proposed system 3.1 Overview 3.2 Functional requirements 3.3 Nonfunctional requirements 3.4 Constraints (“Pseudo requirements”) 3.5 System models 3.5.1 Scenarios 3.5.2 Use case model 3.5.3 Object model 3.5.3.1 Data dictionary 3.5.3.2 Class diagrams 3.5.4 Dynamic models 3.5.5 User interface 4. Glossary

  23. Section 3.5 System Model • 3.5.1 Scenarios • As-is scenarios, visionary scenarios • 3.5.2 Use case model • Actors and use cases • 3.5.3 Object model • Data dictionary • Class diagrams (classes, associations, attributes and operations) • 3.5.4 Dynamic model • State diagrams for classes with significant dynamic behavior • Sequence diagrams for collaborating objects (protocol) • 3.5.5 User Interface • Navigational Paths, Screen mockups • Prototypes Done.

  24. Nonfunctional Requirements: Trigger Questions (1/4) • 3.3.1 User interface and human factors • What type of user will be using the system? • Will more than one type of user be using the system? • What sort of training will be required for each type of user? • Is it particularly important that the system be easy to learn? • Is it particularly important that users be protected from making errors? • What sort of input/output devices for the human interface are available, and what are their characteristics? • 3.3.2 Documentation • What kind of documentation is required? • What audience is to be addressed by each document? • 3.3.3 Hardware considerations • What hardware is the proposed system to be used on? • What are the characteristics of the target hardware, including memory size and auxiliary storage space?

  25. Nonfunctional Requirements: Trigger Questions (2/4) • 3.3.4 Performance characteristics • Are there any speed, throughput, or response time constraints on the system? • Are there size or capacity constraints on the data to be processed by the system? • 3.3.5 Error handling and extreme conditions • How should the system respond to input errors? • How should the system respond to extreme conditions? • 3.3.6 System interfacing • Is input coming from systems outside the proposed system? • Is output going to systems outside the proposed system? • Are there restrictions on the format or medium that must be used for input or output?

  26. Nonfunctional Requirements: Trigger Questions (3/4) • 3.3.7 Quality issues • What are the requirements for reliability? • Must the system trap faults? • What is the maximum time for restarting the system after a failure? • What is the acceptable system downtime per 24-hour period? • Is it important that the system be portable (able to move to different hardware or operating system environments)? • 3.3.8 System Modifications • What parts of the system are likely candidates for later modification? • What sorts of modifications are expected? • 3.3.9 Physical Environment • Where will the target equipment operate? • Will the target equipment be in one or several locations? • Will the environmental conditions in any way be out of the ordinary (for example, unusual temperatures, vibrations, magnetic fields, ...)?

  27. Nonfunctional Requirements: Trigger Questions (4/4) • 3.3.10 Security Issues • Must access to any data or the system itself be controlled? • Is physical security an issue? • 3.3.11 Resources and Management Issues • How often will the system be backed up? • Who will be responsible for the back up? • Who is responsible for system installation? • Who will be responsible for system maintenance?

  28. Constraints (Pseudo Requirements) • Constraint: • Any client restriction on the solution domain • Examples: • The target platform must be an IBM/360 • The implementation language must be COBOL • The documentation standard X must be used • A dataglove must be used • ActiveX must be used • The system must interface to a papertape reader

  29. Modeling Checklist for the Review • Is the model correct? • A model is correct if it represents the client’s view of the the system: Everything is the model represents an aspect of reality • Is the model complete? • Every scenario through the system, including exceptions, is described. • Is the model consistent? • The model does not have components that contradict themselves (for example, deliver contradicting results) • Is the model unambiguous? • The model describes one system (one reality), not many • Is the model realistic? • The model can be implemented without problems

  30. Prioritizing requirements • High priority (“Core requirements”) • Must be addressed during analysis, design, and implementation. • A high-priority feature must be demonstrated successfully during client acceptance. • Medium priority (“Optional requirements”) • Must be addressed during analysis and design. • Usually implemented and demonstrated in the second iteration of the system development. • Low priority (“Fancy requirements”) • Must be addressed during analysis (“very visionary scenarios”). • Illustrates how the system is going to be used in the future if not yet available technology enablers are available

  31. Class-diagrams have different types of „users“ • According to the development activity, the developer plays different roles. • User, User Advocate • Analyst • System-Designer, Detailed Designer • Implementer • In small systems some of the roles do not exist or are played by the same person. • Each of these roles has a different view about the models Application Domain Model Solution Domain Model

  32. Application domain vs. solution domain • Application domain: • The problem domain (financial services, meteorology, accident management, architecture, …). • Application domain class • An abstraction in the application domain. If we model business applications, these classes are also called business objects. • Example: Board game, Tournament • Solution domain • Domains that help in the solution of problems (tele-communication, data bases, compiler construction, operating systems, ….) • Solution domain class • An abstraction, that is introduced for technical reasons, because it helps in the solution of a problem. • Examples: Tree, Hashtable, Scheduler

  33. The Role of the Analyst • The analyst is interested • in application classes: The associations between classes are relationships between abstractions in the application domain. • whether the use of inheritance in the model reflect the taxonomies in the application domain. • Definition Taxonomy: A hierarchy of abstractions • The analyst is not interested • in the exact signature of operations • in solution classes

  34. The User and the User Advocate • User • Creates requirements (together with the Analyst) • Has Application Know How • User Advocate • Mediates between user and analyst • Very important job • The more the user is involved into design the more the user advocate is needed (Participatory Design) • Background • Technical interested user or • analyst who knows the application domain very well

  35. Summary • From use cases to class diagrams • Model and Reality • Activities during Object Modeling • Object and Class Identification • entity, boundary and control objects • Abbott’s technique helps in object identification • Users of class diagrams • Dynamic modeling • Sequence diagrams • State diagrams • Using dynamic modeling for the design of user interfaces • Non-functional requirements analysis • Requirements analysis model validation • Roles within the Analysis Process

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