SYSTEMS ANALYSIS CIS 3300
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This 26 page Class Notes was uploaded by Jalyn Heaney DDS on Monday September 21, 2015. The Class Notes belongs to CIS 3300 at Georgia State University taught by Staff in Fall. Since its upload, it has received 30 views. For similar materials see /class/209820/cis-3300-georgia-state-university in Computer Information Systems at Georgia State University.
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Date Created: 09/21/15
Introduction to Use Cases Requirements to Use Cases Use Case Basics Some Use Case Details In Class Use Cases Discussion Questions 1998 William N Robinson Questions Answered in This Lecture 0 What is the relationship between requirements and use cases 0 What is a Use Case What Is a Model A model is an abstract representation of reality that containsportrays only important aspects of the h omenon being studied 4 39b And by default omits unnecessa detail and superfluous elements Modeling Modeling Requirements Data Processes E ObjectOriented Analysis Textual documentation Describes system Rationale Requirements 0 Multiple system models Processing depicted in different views Use case diagram graph Contracts text Data depicted depicted in different views Conceptual model graph l Class diagram graph Requirements to Use Cases Traceability from Requirements to Behaviors For each active requirement there should be at least one use case that implements it For each use case there should be at least one requirement that it implements Use Case Basics Use Case Diagram POST shall compute a running total of sales item for the current transaction 0 POST shall pro ide secure access to its functions This is a nonfunctional requirement 0 POST shall allow for the itemized refund of previously purchased items V Use Case Basics Documenting a Use Case simpli ed Use Case Buy Items 0 Actors Customer Cashier Type Primary 0 Purpose Assist and record a sale Description A customer arrives at a checkout with items to purchase The Cashier records the purchased items and collects a payment On completion the customer leaves with the items Typical Course of Events Actor Action System Response 0 X does y system does 2 0 The Use of Use Cases Informal technique for capturing basic functions Adopted in various forms by all the major 00 methodologies Users and Developers have complementary view of Use Cases Users 0 Can read understand and critique business level use casesscenarios Developer 0 Good for basic structure and interaction of application parts Use Case Definition Use Case a sequence of transactions in a system whose task is to yield a measurable value to an individual actor of the system a pattern of behavior that the system exhibits Each use case is a sequence of related transactions performed by an actor and the system in a dialogue 2 Notation Actor a role that someone or something in the environment can play in relation to the business everything that interacts with the system the same someone or something can play different Jambs m 8 1995 roles Use Cases Details Use Case Elements Transaction an atomic set of activities that is performed either fully or not at all invoked by a stimulus consists of actions decisions and transmission of stimuli A measurable value performance has a visible quantifiable andor qualifiable impact on things outside the system and in particular the actor who initiated the task Use Cases Details Documenting Use Cases 0 A flow of events document is created for each use cases Written from an actor point of view Details what the system must provide to the actor when the use cases is executed Typical contents How the use case starts and ends Normal flow of events Alternate flow of events Exceptional flow of events Use Cases Details Buy Items with Ca sh Typical Events 1 This use case begins when a Customer arrives at a POST checkout with items to purchase 2 The Cashier records the identi er for each item If there is more than one of the same item the 3 Determines the item price and adds Cashier can enter the quantity as well the item information to the running sales transaction 4 On completion of the item entry the Cashier indicates to the POSI39 that item entry is Zhesnetsig 39gneanisg zgf the complete U I r pr 6 The Cashier tell the Customer the total 5 calculates and presents the sale tom 7 The Customer gives a cash paymentthe cash tenderedquot possibly greater than the sale total 8 The Cashier records the cash received amount 10 The Cashier deposits the cash received and 9 srgwsotnq balance due baCk to the extracts the balance owing The Cashier gives Gzneraters a recei t the balance owing 8i printed receipt to p CUStOfl39ler 11 Logs the completed sale 12 The Customer leaves Alternative Line 2 Invalid identifier entered Indicate error Courses Line 7 Customer didn t have enough cash Cancel sales transaction Use Case Structure 0 Dozens Not hundreds Contains Brief statement of purpose 1 sunny day event main course primary scenario N rainy days alternate courses secondary scenarios Complete end to end business process From initiation to completion Initiated at an external interface Common error Use Case for an individual step in a process rather than a complete end end process that starts at the interface Distribution of Submarine Supplies Requirements We are losing business due to our poor order processing and delivery We mainly serve as a distribution center that consolidates produce and meats for submarine shops However we are not meeting our business objectives of profit quality responsiveness Moreover we are not as efficient as we would like as our works spend an inordinate amount of time trying to use our current system Things are a bit chaotic now Your assignment Consider component systems of business such as a Distribution Center a Financial Center and Franchise Support Dunmcunslderlhe PulnlulSaleTermmal Draw a Use Case Diagram Document a Use Case Discussion Discussion Questions How detailed should a Use Case be How are Use Cases related to each other Are there Use Cases for Design as well as analysis Planning in Project Management Project Planing Gantt Chart PERT Chart In Class Project Plan A Person month Illustration Mythical Man month Discussion 1998 William N Robinson Questions Answered in This Lecture What is project planning What techniques are used to form and analyze a plans What kind or problems arise during the execution of a project plan What is the mythical man month The Project Management Definition The process of planning directing and controlling the development of an acceptable system at a ninimum cost within a specified time frame WhineI etal I9 3 Project Planning The Project Plan 0 Used for 0 Includes Communicating schedules Estimates of Scheduling Human effort person t Determine estimated time mo 5 4 required for project 39 Chronomglcal PI39OJSCt duration months Derive actual dates and allocate resources 39 C 5t donars control Project schedule Identiw current and 39 TaSk aSSiQnment potential problems u Milestones Project Planning Estimate Resources Required skills E Availabiliw Duration of tasks Start date People Description igt Availability Duration of use Delivew date Hardwaresoftware Project Planning Project Planning Techniques Two classic techniques Gantt charts PERT charts The Gantt Chart FEB On time Gantt Chart The Gantt Chart Tasks Assigned Curly M0 M0 Larry Curly Curly Mo Hy Curly Mo PERT Charts Project Evaluation and Review Technique Plan and control of large projects Shows interdependence of project tasks Organized in terms of 0 Events Tasks Graphical networking technique PERT Chart PERT Definitions 0 Event Also known as a milestone A point in time at startend of tasks A node on the chart 0 Task A project activity or set of activities A link between two events Labeled with expected duration Dunnnytask A dependency between events with no activity PERT Chart PERT Notation Milestone Earliest completio date Latest completion Event date the absolute deadline Contingency Factor latest earliest Task 0 Task identification I number Expected I I duration PERT Chart A Typical PERT Chart Max of parallel tasks Difference of earlie from max of parallel tasks PERT Chart Deriving a PERT Chart 0 Make a list of tasks and events 9 Determine inter task dependencies 9 Estimate duration of tasks 9 Derive earliest and latest completion times 9 Draw chart PERT Chart Table Form of PERT Chart PERT Chart Drawing a PERT Chart PERT Chart The Critical Path The critical path is V A sequence of dependent project tasks that have the largest sum of estimated duration s Also known as a path with no slack time built in Path along which any delay will delay the whole project PERT Chart Determining the Critical Path 0 Identify all task paths that exist A inteniew DFD dummy SC test dummy install B A inteniew ERD dummy SC test dummy install C inteniew DFD dummy SC code dummy install D A inteniew ERD dummy SC code dummy install 9 Calculate the total expected duration time for each path Sum the task expected durations 9 Identify the critical path as the one with the largest expected duration time PERT Chart ritical Path Example Paths 21 14b 13 c 16 d 15 PERT Chart Using the Project Plan Assign staff Give senior people the difficult tasks Create a schedule Give senior people the critical tasks I a Create a Project Plan Your assignment You have 10 minutes Create a project plan for your class project 0 Use gantt or PERT Based on this term Include all major tasks 3 Assign members to tasks 9 Q a You will need to create and complete such a chart for your project The Personmonth What is it A unit of scheduling the amount of work able to be completed by one person in one month Assumptions All workers are equal A project can be cleanly divided into tasks 0 Truth Cost is proportional to people and months Fallacy Effort is not proportional to people and months A PersonMonth Illustmtion A Small Schedule Problem A project has been estimated at 12 person months 12 month 3 person 4 month person Three persons have been assigned to the project There are four tasks each scheduled to take one month 0 3 person months each How long should the project take to complete 4 months l l A PersonMonth Illustmtion The Schedule Slips The first milestone is not reached until the end of the second month Now what Complete the project on time Complete the project late 0 We have two months to complete three tasks scheduled to take three months to complete How many person months remain to be completed 2 months months A PersonMonth Illustmtion First Assumption Only Task One Was Ml39sestmated 0 Nine personmonths remain to be completed Originally there were 4 tasks each scheduled to take 1 month each 0 3 personmonths per task Assume the remaining tasks were estimated correctly 0 3 tasks remain each at 3 personmonths 9 PM Original 4 months 2 m nths 2 months more l l E But we only have 3 people and 2 months remaining on original scheduled so We need 45 people WP 9PM2M Solution add 2 people to the project to bring the total to 5 people A PersonMonth Illustmtion Second Assumption Each Task Was Msesz imaz ea o 18 personmonths remain to be completed Originally there were 4 tasks each scheduled to take 1 month each 0 3 personmonths per task Assume the remaining tasks were estimated incorrectly o 3 tasks remain each at 6 personmonths 18 PM Original 4 months 2 m nths 2 months more But we only have 3 people and 2 months remaining on original scheduled so We need 9 people XPP 18PM2M Solution add 6 people to the project to bring the total to 9 people A PersonMonth Illustmtion Are There Any Alternatives Reschedule Scale back Overtime Productivity ought to mean achieving more in an hour of work often it means achieving more in an hour of pay Managers divide the work done by 40 hours rather than the 60 hours spent on the job This isn t productivity it s fraud Perfectly Partitionable Task 1 2 3 4 5 6 7 8 9 10 Persons Mythical Man Month Unpartitionable Task 1 2 3 4 5 6 7 8 9 10 Person Mythical Man Month Why Is Partitioning So Difficult Dif cult to create non overlapping tasks New participants must be trained Communication paths multiply How many different communication paths are there in a group of N people How many more are added when the N1 person joins the group Mythical Man Month Brook s Law 0 Adding people to a late project makes it later Effort LOC N N 12 simplified wo constants c LOC is lines of code N is the number of people on a project N N 12 account for the coordination and communication among the project members Brook s Law r fort V I meat Law Lme ot Lode Mythical Man Month Programmers Not Factory Workers Factory assembly line work is serializable and independent Software work is partially parallel and interdependent N 20 u quot215 lU10 rP e5 0 f o e 9 9 Person Work Produced Mythical Man Month Mythical Personmonth Adding people to a late project can make it later Training new members Reduced group effectiveness Mythical Man Month Scheduling Problems 0 Good intentions go wrong People tend to be optimistic It will work right the rst time Probability that it will work right the rst time is dependent upon all tasks that came before it working right People want to make others happy Poor estimates from analysts to management and from management to customer create unrealistic expectations 0 Schedule estimation techniques are poorly developed Assumption that effort progress is wrong 0 Schedule progress is poorly monitored Mythical Man Month Summary Projects must be planned There is not a direct linear trade off between people on a project and the number of months it takes to complete a project Discussion Discussion Questions I believe that large programming projects suffer management problems different in kind from small ones FP Brooks Jr Do you agree Elaborate What can be done to overcome problems of larger projects Mythical Man Month A Focus on the Team Manage communication complexity CASE tools facilitate group work 5 Reduces lines of communication Group paradigms and roles EG Chief programmer model Solves communication complexiw Good with super programmers Does not address benefits of teams
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