Modelling Concepts Roman Kontchakov Birkbeck, University of London - PowerPoint PPT Presentation

Information Systems Concepts Modelling Concepts Roman Kontchakov Birkbeck, University of London Based on Chapter 5 and 7 of Bennett, McRobb and Farmer: Object Oriented Systems Analysis and Design Using UML, (4th Edition), McGraw Hill, 2010 1

Outline  Models and Diagrams  Section 5.2 (pp. 114 – 122)  What Must a Requirements Model Do?  Section 7.2 (pp. 181 – 184) 2

What is a Model?  “A model captures a view of a physical system. It is an abstraction of the physical system, with a certain purpose . This purpose determines what is to be included in the model and what is irrelevant. Thus the model completely describes those aspects of the physical system that are relevant to the purpose of the model, at the relevant level of detail .” (OMG, 2009) 3

What is a Model? Business Model Program Systems Analysis and Design Coding Conceptual world Computing world Real world 4

Abstraction 5

Why use a model?  A model is quicker and easier to build  A model can be used in a simulation  A model can evolve as we learn  We can choose which details to include in a model  A model can represent real or imaginary things from any domain  A model allows us to talk, or reason, about the real thing without actually building it  Much of software development involves creating and refining models, rather than writing lines of code 6

Requirements model  describes what the software should do  represents people, things and concepts important to understand what is going on  shows connections and interactions among these people, things and concepts  shows the business situation in enough detail to evaluate possible designs  must be organized so as to be useful for designing the software 7

What is a Diagram?  A diagram is a graphical representation of a set of elements in the model of the system  Models v Diagrams  A diagram illustrates some aspect of a system  A model provides a complete view of a system at a particular stage and from a particular perspective  Most IS models today are in the form of diagrams, with supporting textual descriptions and logical or mathematical specifications  A model usually contains many diagrams – related to one another in some way 8

Why use a diagram?  Natural language is often too ambiguous to be used for modeling  Communication + Ambiguity = Confusion ! A large object with one trunk and four legs. 9

UML Diagrams  UML 2 defines 13 types of diagrams  Structure  Class Diagram , Object Diagram  Component Diagram, Package Diagram  Composite Structure Diagram, Deployment Diagram  Behaviour  Use Case Diagram  Activity Diagram, State Machine Diagram  Interaction  Sequence Diagram , Communication Diagram  Timing Diagram, Interaction Overview Diagram See Also: Appendix A – Notation Summary 10

UML diagrams notation  A UML diagram usually consists of:  icons  symbols Plan Chapter  paths Produce  strings First Draft Revise Draft [not satisfied] [satisfied] Add Exercises Add References to Bibliography 11

What models/diagrams are good?  Accurate  unambiguous , following rules or standards  Concise  showing only what needs to be shown  Complete  showing all that needs to be shown  Consistent  internally and among each other  Hierarchical  breaking the system down into different levels of details 12

Developing models  During the life of a project using an iterative lifecycle, models change along the dimensions of:  abstraction — they become more concrete  formality — they become more formally specified  level of detail — additional details are added 13

Example: Development of a Use Case model Staff Management Iteration 1 Add a new staff Staff Management member Add a new staff member Add a new staff grade Add a new staff grade Change the rate for a staff grade Obvious use cases Accountant Change the rate for a staff grade Change the grade for a staff member Accountant Change the grade for a staff member Calculate staff bonuses Calculate staff bonuses Simple use case descriptions Iteration 2 Staff Management Add a new staff member Staff Management Add a new staff Staff Management member Add a new staff grade Campaign Selection Add a new staff Additional use cases member Add a new staff Campaign Selection grade Change the Holborn Motors rate for a Client: staff grade Campaign Selection Lynch Properties Add a new staff grade Holborn Motors Accountant Change the Yellow Partridge Yellow Partridge rate for a Client: Lynch Properties staff grade Change the Zeta Systems Holborn Motors grade for a Yellow Partridge Yellow Partridge Change the staff member Client: Spring Jewellery Campaign 1997 Accountant Lynch Properties Zeta Systems rate for a Campaign: Spring Jewellery Campaign 2001 staff grade Change the Yellow Partridge grade for a Spring Jewellery Campaign 1997 staff member Zeta Systems Spring Jewellery Campaign 2002 Accountant Calculate staff Campaign: bonuses Spring Jewellery Campaign 2001 Summer Collection 1998 Simple use case descriptions Change the grade for a Spring Jewellery Campaign 2002 Spring Jewellery staff member Campaign: Calculate staff Summer Collection 1998 Campaign 2002 bonuses OK Quit Calculate staff OK Quit bonuses OK Quit Prototypes Iteration 3 amp C aig n Managem en t Assign staff to work on a campaign «include» amp C aig n Man agement Find campaign Structured use cases ssign s A taff «inc lude» to wo a campaign rk on Add a n ew Campaign Selection «include» advert to Cam paign Man ag a campaign ement ind cam F paign «include» Assign staff Campaign «include» Campaign Selection to work on Manager Add a new Holborn Motors a campaign «include» advert to a campaign «include» Chec k campaign budget Client: Find campaign Campaign Selection Lynch Properties Campaign «inclu de» Manag er Holborn Motors Yellow Partridge A advert to dd a new «ex tend» «extend» Client: Yellow Partridge a campaign Check campaign Lynch Properties «include» budge t Zeta Systems rint campaign P Print campaign Holborn Motors Yellow Partridge C ampaign summar y inv oice Client: Yellow Partridge Manager «extend» «extend» Lynch Properties Spring Jewellery Campaign 1997 Check campaign Zeta Systems budge t Accountant Campaign: Spring Jewellery Campaign 2001 Yellow Partridge Structured use case descriptions Pr summary int campaign Print campaign invoice Spring Jewellery Campaign 1997 Spring Jewellery Campaign 2002 Zeta Systems «extend» «extend» Campaign: Spring Jewellery Campaign 2001 Summer Collection 1998 Accountant int campaign Pr Print campaign Spring Jewellery Campaign 2002 Spring Jewellery summary invoice Campaign: Summer Collection 1998 Campaign 2002 OK Quit Accountant OK Quit OK Quit Prototypes 14

Take Home Messages  Models  Diagrams 15