Tutorial notes on. Requirements analysis

Transcription

1 Tutorial notes on Requirements analysis Dr. C. Constantinides, P.Eng. Computer Science and Software Engineering Concordia University Page 1 of 12

2 Exercise 1. Consider an client software. The client has one mailbox which consists of a number of diferent folders. Each folder contains a number of messages. A message cannot exist in more than one folders. A user can invoke a view on a message and in fact a user may have various views, each corresponding to one message. (a) Illustrate the appropriate mechanisms in order to identify concepts and their associations. (b) Create a domain model for the client. (c) Define the term multiplicity expression and show its applicability on the domain model. (d) Define the term aggregation (and its different types) and clearly illustrate its applicability to the domain model. Solution: (a) Domain model 1. Noun-phrase identification: Mailbox, Folder, Message, View 2. Conceptual class category list: Containers of other things: (Mailbox, Folder), (Folder, Message). 3. Common associations list: A logical part of B: (Mailbox, Folder), (Message, Folder) A is a description of B: (View, Message) A is captured in B: (View Message) (b) The domain model is shows below: 1 (c) The following is defined as follows: Multiplicity: How many instances of one type may be associated with an instance of another type at one point in time. Mailbox Folder: one-to-many, Folder-Message: one-to-many, Page 2 of 12

3 Message-View: one-to-many (d) The following terms are defined as follows: Aggregation: defines a whole-part association. Composite aggregation: multiplicity at composite end is 1. Mailbox-Folder, Folder-Message. Shared aggregation: Multiplicity at composite end is more than one. Page 3 of 12

4 Exercise 2. Our system is the Registrar office of a University where students go in order to enroll for classes. Consider the following success scenario of use case Process Registration: A student arrives at the Registrar s office in order to enroll in one or more classes. The clerk will access the terminal in order to initiate a new enrollment session (you may assume that they already have been authenticated by the system). Each enrollment session captures the date and time it was initiated. The clerk will proceed to enroll the student in each class requested. For each class, the clerk will enter the student name and identification number and the class identification number. In response to each entry, the system will display a description and a confirmation. At the end of the session, the system will display a confirmation of the procedure and the total amount of tuition fees due. The clerk will then initiate a payment of tuition fees and the system will respond with the change due and a receipt. (a) Create a domain model based on the above scenario. (b) Describe what a system sequence diagram (SSD) is and create one with respect to the above scenario. Use the SSD to define the terms system event and system operation and public system interface. (c) Define the terms operation contract, precondition, and postcondition, and create an operation contract for the system operation deployed to initiate the enrollment session. Clearly illustrate the relationships between the operation contract and the domain model. Page 4 of 12

5 Solution: (a) The domain model is shown below: Page 5 of 12

6 (b) A System Sequence Diagram (SSD) is a diagram that shows, for a particular scenario of a use case, the interactions between an actor the the system as a black box. The SSD is shown below: The following terms are defined as follows: 1. System event: message (request) generated by actrors to system. 2. System operation: Operations that the system (as a black box) offers in its public interface to handle incoming system events. 3. Public system interface: the entire set of system operations across all use cases. (c) The following terms are defined as follows: 1. Operation contract: Document that describes system behavior. 2. Precondition: Assumption about the state of the system before execution of the operation. 3. Postcondition: Assumption that refer to the state of the system after completion of the operation. (creation/deletion of instances, formation/bgreaking of associations, modification of attribute) Page 6 of 12

7 The operation contract for addenrollment is as follows: Contract CO1: addenrollment Operation: addenrollment () Cross References: Use Cases: Process Registration. Pre-conditions: Clerk has been authenticated by the system. Post-conditions: 1. An Enrollment instance e was created. (instance creation) 2. e was associated with Student (association formed) 3. e was associated with Class (association formed) 4. e was associated with EnrollmentCatalog (association formed) 5. Attributes of e were initialized (modification of attribute) Page 7 of 12

8 Exercise 3. Consider a system contains a catalog (database) with books and journals. A library clerks access the system in order to populate the catalog to search the catalog to complete a booking to handle returns Library members access the system in order to search the catalog. The UML use case diagram is shown below: Below is the use case Process Entry: Use Case: Actor: Pre-condition: Post-condition: UC1 - Process Entry Library clerk Clerk is identified and authenticated Entered valid entries are stored in catalog. Page 8 of 12

9 Success scenario (basic flow): 1. Library clerk starts a session from a terminal for populating the catalog. 2. Clerk enters required information for a book. 3. System validates and stores the information and confirms of the success of the operation. 4. Clerk repeats step 2-3 until indicates done. Extensions (alternative flow): 3a. If data is invalid, then system informs clerk of the error. The UML system sequence diagram for the success scenario of this use case is shown below: The set of all required system operations is determined by identifying the system events: makenewentry() addbook() endentry() Page 9 of 12

10 In order to build a domain model, we first need to identify conceptual classes. We can do this by 1. Use noun phrase identification. Identify noun (and noun phrases) in textual descriptions of the problem domain, and consider them as concepts or attributes. Use cases are excellent description to draw for this analysis. 2. Use a conceptual class category list as follows: Concept Category Physical or tangible objects Places Transactions Transaction line items Roles of people Containers of other things Example Terminal, Book Library Populate Catalog, Search Catalog Booking item Library Clerk, Library Member Library, Catalog We can use a common associations list in order to find associations between conceptual classes: Category A is a physical part of B A is a logical part of B A is physically contained in/on B A is logically contained in B Examples Drawer Terminal Book Entry Terminal - Library Book - Catalog A is a line item of a transaction or report B Book Entry A is known/logged/recorded/ captured in B Terminal - Entry Terminal Catalog Entry - Catalog A is a member of B Library Clerk - Library Page 10 of 12

11 The domain model is shown below: We now need to define contracts for system operations. Nore that the entire set of system operations across all use cases, defines the public system interface. In the UML the system as a whole can be represented as a class. Contracts are written for each system operation to describe its behavior. The contracts are shown below: Contract CO1: Operation: Cross References: Pre-conditions: Post-conditions: makenewentry makenewentry() Use case Process Entry. None. 1. an instance of Entry e was created (instance creation) 2. e was associated with Terminal (formation of association) 3. e was associated with Catalog (formation of association) Page 11 of 12

12 Contract CO2: Operation: Cross References: Pre-conditions: Post-conditions: addbook addbook(author, title, publisher, year) Use case Process Entry. Am entry is under way. 1. an instance of Book b was created (instance creation). 2. b was associated with Catalog (formation of association) 3. Attributes in b have been modified. Contract CO3: Operation: Cross References: Pre-conditions: Post-conditions: endentry endentry() Use case Process Entry. An entry is under way. Attribute Entry.isComplete was set to true (modification of attribute) Page 12 of 12