CH5_System modeling.pptx

Chapter 5 – System Modeling Chapter 5 System Modeling 1 Topics covered  Context models  Interaction models  Structural models  Behavioral models Chapter 5 System Modeling 2 System modeling  System modeling is the process of developing abstrac...

Chapter 5 – System Modeling Chapter 5 System Modeling 1 Topics covered  Context models  Interaction models  Structural models  Behavioral models Chapter 5 System Modeling 2 System modeling  System modeling is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system.  System modeling has now come to mean representing a system using some kind of graphical notation, which is now almost always based on notations in the Unified Modeling Language (UML).  System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers. Chapter 5 System Modeling 3 Existing and planned system models  Models of the existing system are used during requirements engineering. They help clarify what the existing system does and can be used as a basis for discussing its strengths and weaknesses. These then lead to requirements for the new system.  Models of the new system are used during requirements engineering to help explain the proposed requirements to other system stakeholders. Engineers use these models to discuss design proposals and to document the system for implementation.  In a model-driven engineering process, it is possible to generate a complete or partial system implementation from the system model. Chapter 5 System Modeling 4 System perspectives  An external perspective, where you model the context or environment of the system.  An interaction perspective, where you model the interactions between a system and its environment, or between the components of a system.  A structural perspective, where you model the organization of a system or the structure of the data that is processed by the system.  A behavioral perspective, where you model the dynamic behavior of the system and how it responds to events. Chapter 5 System Modeling 5 UML diagram types  Activity diagrams, which show the activities involved in a process or in data processing.  Use case diagrams, which show the interactions between a system and its environment.  Sequence diagrams, which show interactions between actors and the system and between system components.  Class diagrams, which show the object classes in the system and the associations between these classes.  State diagrams, which show how the system reacts to internal and external events. Chapter 5 System Modeling 6 Use of graphical models  As a means of facilitating discussion about an existing or proposed system  Incomplete and incorrect models are OK as their role is to support discussion.  As a way of documenting an existing system  Models should be an accurate representation of the system but need not be complete.  As a detailed system description that can be used to generate a system implementation  Models have to be both correct and complete. Chapter 5 System Modeling 7 Context models Chapter 5 System Modeling 8 Context models  Context models are used to illustrate the operational context of a system - they show what lies outside the system boundaries.  Social and organisational concerns may affect the decision on where to position system boundaries.  Architectural models show the system and its relationship with other systems. Chapter 5 System Modeling 9 System boundaries  System boundaries are established to define what is inside and what is outside the system.  They show other systems that are used or depend on the system being developed.  The position of the system boundary has a profound effect on the system requirements.  Defining a system boundary is a political judgment  There may be pressures to develop system boundaries that increase / decrease the influence or workload of different parts of an organization. Chapter 5 System Modeling 10 The context of the Mentcare system Chapter 5 System Modeling 11 Process perspective  Context models simply show the other systems in the environment, not how the system being developed is used in that environment.  Process models reveal how the system being developed is used in broader business processes.  UML activity diagrams may be used to define business process models.  Activity diagrams are intended to show the activities that make up a system process and the flow of control from one activity to another. Chapter 5 System Modeling 12 Process model of involuntary detention Chapter 5 System Modeling 13 Structural models Chapter 5 System Modeling 14 Structural models  Structural models of software display the organization of a system in terms of the components that make up that system and their relationships.  Structural models may be static models, which show the structure of the system design, or dynamic models, which show the organization of the system when it is executing.  You create structural models of a system when you are discussing and designing the system architecture. Chapter 5 System Modeling 15 Class diagrams  Class diagrams are used when developing an object- oriented system model to show the classes in a system and the associations between these classes.  An object class can be thought of as a general definition of one kind of system object.  An association is a link between classes that indicates that there is some relationship between these classes.  When you are developing models during the early stages of the software engineering process, objects represent something in the real world, such as a patient, a prescription, doctor, etc. Chapter 5 System Modeling 16 UML classes and association Chapter 5 System Modeling 17 Classes and associations in the MHC-PMS Chapter 5 System Modeling 18 The Consultation class Chapter 5 System Modeling 19 Generalization  Generalization is an everyday technique that we use to manage complexity.  Rather than learn the detailed characteristics of every entity that we experience, we place these entities in more general classes (animals, cars, houses, etc.) and learn the characteristics of these classes.  This allows us to infer that different members of these classes have some common characteristics e.g. squirrels and rats are rodents. Chapter 5 System Modeling 20 Generalization  In modeling systems, it is often useful to examine the classes in a system to see if there is scope for generalization. If changes are proposed, then you do not have to look at all classes in the system to see if they are affected by the change.  In object-oriented languages, such as Java, generalization is implemented using the class inheritance mechanisms built into the language.  In a generalization, the attributes and operations associated with higher-level classes are also associated with the lower-level classes.  The lower-level classes are subclasses inherit the attributes and operations from their superclasses. These lower-level classes then add more specific attributes and operations. Chapter 5 System Modeling 21 A generalization hierarchy Chapter 5 System Modeling 22 A generalization hierarchy with added detail Chapter 5 System Modeling 23 Object class aggregation models  An aggregation model shows how classes that are collections are composed of other classes.  Aggregation models are similar to the part-of relationship in semantic data models. Chapter 5 System Modeling 24 The aggregation association Chapter 5 System Modeling 25 Interaction models Chapter 5 System Modeling 26 Interaction models  Modeling user interaction which involves user inputs and outputs.  It helps to identify user requirements.  Modeling system-to-system interaction highlights the communication problems that may arise.  Modeling component interaction helps us understand if a proposed system structure is likely to deliver the required system performance and dependability.  Use case diagrams and sequence diagrams may be used for interaction modelling. Chapter 5 System Modeling 27 Use case modeling  Use cases were developed originally to support requirements elicitation and now incorporated into the UML.  Each use case represents a discrete task that involves external interaction with a system.  A use case is shown as an ellipse  The actors may be people or other systems involved in the use case  Represented as stick figures. Chapter 5 System Modeling 28 Transfer-data use case  A use case in the Mentcare system Chapter 5 System Modeling 29 Use case modeling  Use case diagrams give a fairly simple overview of an interaction so you have to provide more detail to understand what is involved.  This detail can either be a simple textual description, a structured description in a table, or a sequence diagram Chapter 5 System Modeling 30 Tabular description of the ‘Transfer data’ use- case MHC-PMS: Transfer data Actors Medical receptionist, patient records system (PRS) Description A receptionist may transfer data from the Mentcare system to a general patient record database that is maintained by a health authority. The information transferred may either be updated personal information (address, phone number, etc.) or a summary of the patient’s diagnosis and treatment. Data Patient’s personal information, treatment summary Stimulus User command issued by medical receptionist Response Confirmation that PRS has been updated Comments The receptionist must have appropriate security permissions to access the patient information and the PRS. Chapter 5 System Modeling 31 Use cases in the Mentcare system involving the role ‘Medical Receptionist’ Composite use case diagram Chapter 5 System Modeling 32 Sequence diagrams  Sequence diagrams are part of the UML and are used to model the interactions between the actors and the objects within a system.  A sequence diagram shows the sequence of interactions that take place during a particular use case or use case instance.  The objects and actors involved are listed along the top of the diagram, with a dotted line drawn vertically from these.  Interactions between objects are indicated by annotated arrows. Chapter 5 System Modeling 33 The name of the participant can be: A named instance (like here) An anonymous instance (no object Sequence Diagram Notation name, but class name required) A class if interaction through class Interaction operations (class scope): not between underlined participating objects anObjectName:MyClas otherObjectName:MyOtherCla s ss Send event: the Receive event: Execution occurrence: message is sent the message is something executes received Notice the colon with a start and an separating the end. message object name from Also called execution the class name bar. Message Interaction label through message passing Return message The object’s lifeline (optional) (time flows downward) Chapter 5 System Modeling 34  Example of Sequence with Code :A myB:B What might this represent doOne in code? e.g. java doTwo public class A { private B myB = new B(); doThree public void doOne() { Sequence myB.doTwo(); diagram myB.doThree(); } //... } Chapter 5 System Modeling 35  Sequence diagram for View patient information Alternative Fragment Chapter 5 System Modeling 36  Sequence diagram for Transfer Data Chapter 5 System Modeling 37 Behavioral models Chapter 5 System Modeling 38 Behavioral models  Behavioral models are models of the dynamic behavior of a system as it is executing. They show what happens or what is supposed to happen when a system responds to a stimulus from its environment.  You can think of these stimuli as being of two types:  Data Some data arrives that has to be processed by the system.  Events Some event happens that triggers system processing. Events may have associated data, although this is not always the case. Chapter 5 System Modeling 39 Data-driven modeling  Many business systems are data-processing systems that are primarily driven by data. They are controlled by the data input to the system, with relatively little external event processing.  Data-driven models show the sequence of actions involved in processing input data and generating an associated output.  They are particularly useful during the analysis of requirements as they can be used to show end-to-end processing in a system. Chapter 5 System Modeling 40  An activity model of the insulin pump’s operation Rectangles: Input/Output Rounded Rectangles: Activities Chapter 5 System Modeling 41 Order processing Chapter 5 System Modeling 42 Event-driven modeling  Real-time systems are often event-driven, with minimal data processing. For example, a landline phone switching system responds to events such as ‘receiver off hook’ by generating a dial tone.  Event-driven modeling shows how a system responds to external and internal events.  It is based on the assumption that a system has a finite number of states and that events (stimuli) may cause a transition from one state to another. Chapter 5 System Modeling 43 State machine models  These model the behaviour of the system in response to external and internal events.  They show the system’s responses to stimuli so are often used for modelling real-time systems.  State machine models show system states as nodes and events as arcs between these nodes. When an event occurs, the system moves from one state to another.  Statecharts are an integral part of the UML and are used to represent state machine models. Chapter 5 System Modeling 44  State diagram of a microwave oven Nodes: system states Arcs: events Chapter 5 System Modeling 45 Microwave oven operation Chapter 5 System Modeling 46 States and stimuli for the microwave oven (a) State Description Waiting The oven is waiting for input. The display shows the current time. Half power The oven power is set to 300 watts. The display shows ‘Half power’. Full power The oven power is set to 600 watts. The display shows ‘Full power’. Set time The cooking time is set to the user’s input value. The display shows the cooking time selected and is updated as the time is set. Disabled Oven operation is disabled for safety. Interior oven light is on. Display shows ‘Not ready’. Enabled Oven operation is enabled. Interior oven light is off. Display shows ‘Ready to cook’. Operation Oven in operation. Interior oven light is on. Display shows the timer countdown. On completion of cooking, the buzzer is sounded for five seconds. Oven light is on. Display shows ‘Cooking complete’ while buzzer is sounding. Chapter 5 System Modeling 47 States and stimuli for the microwave oven (b) Stimulus Description Half power The user has pressed the half-power button. Full power The user has pressed the full-power button. Timer The user has pressed one of the timer buttons. Number The user has pressed a numeric key. Door open The oven door switch is not closed. Door closed The oven door switch is closed. Start The user has pressed the Start button. Cancel The user has pressed the Cancel button. Chapter 5 System Modeling 48 Deployment Diagram UML deployment diagrams are used to depict the relationship among run-time components and nodes. used to visualize the physical architecture of a system. It shows the hardware and software components involved in the system and how they interact. Deployment diagrams provide a clear picture of how the system will be deployed. Chapter 5 System Modeling 49 Deployment Diagram Key Components: Nodes: are physical entities in the system, typically represented as 3D boxes. They can be devices (like servers, mobile phones, routers) or execution environments (like databases, virtual machines, web servers). Artifacts: are the pieces of software that reside on nodes. These are often applications, libraries, executables, databases, or scripts, and are represented as rectangles within nodes. Chapter 5 System Modeling 50 Deployment Diagram Key Components: Communication Paths: These paths, represented by solid lines, show the communication links or connections between nodes. They indicate how different nodes (hardware devices) interact and communicate, which can be through protocols like HTTP, TCP/IP, etc. Chapter 5 System Modeling 51 Deployment Diagram This example depicts a deployment diagram with a Web browser accessing a Web server. The Web server in turns accesses a database server. Chapter 5 System Modeling 52 Key points  A model is an abstract view of a system that ignores system details. Complementary system models can be developed to show the system’s context, interactions, structure and behavior.  Context models show how a system that is being modeled is positioned in an environment with other systems and processes.  Use case diagrams and sequence diagrams are used to describe the interactions between users and systems in the system being designed. Use cases describe interactions between a system and external actors; sequence diagrams add more information to these by showing interactions between system objects.  Structural models show the organization and architecture of a system. Class diagrams are used to define the static structure of classes in a system and their associations. Chapter 5 System Modeling 53 Key points  Behavioral models are used to describe the dynamic behavior of an executing system. This behavior can be modeled from the perspective of the data processed by the system, or by the events that stimulate responses from a system.  Activity diagrams may be used to model the processing of data, where each activity represents one process step.  State diagrams are used to model a system’s behavior in response to internal or external events.  Model-driven engineering is an approach to software development in which a system is represented as a set of models that can be automatically transformed to executable code. Chapter 5 System Modeling 54