System Modeling Lecture Notes PDF

12/23/2023 System Modeling  Context models  Interaction models  Structural models  Behavioral models  Model-driven engineering Dr. Noha Adly CSE 322 - System Modeling 1 1 ...

12/23/2023 System Modeling  Context models  Interaction models  Structural models  Behavioral models  Model-driven engineering Dr. Noha Adly CSE 322 - System Modeling 1 1  12/23/2023 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.  Models are used during  requirements engineering process to help derive the requirements for a system  design process to describe the system to engineers implementing the system  after implementation to document the system’s structure and operation. Dr. Noha Adly CSE 322 - System Modeling 2 2  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 3 3  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 4 4  12/23/2023 System perspectives  You may develop different models to represent the system from different 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. Dr. Noha Adly CSE 322 - System Modeling 5 5  12/23/2023 UML diagram types  UML has 13 diagrams types, but five could represent the essentials of a system  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. Dr. Noha Adly CSE 322 - System Modeling 6 6  12/23/2023 Context models Dr. Noha Adly CSE 322 - System Modeling 7 7  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 8 8  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 9 9  12/23/2023 The context of the Mentcare system a simple context model that shows the patient information system and the other systems in its environment Dr. Noha Adly CSE 322 - System Modeling 10 10  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 11 11  12/23/2023 Process model of involuntary detention process Dr. Noha Adly CSE 322 - System Modeling 12 12  12/23/2023 Interaction models Dr. Noha Adly CSE 322 - System Modeling 13 13  12/23/2023 Interaction models  Modeling user interaction is important as 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.  Use case modeling, mostly used to model interactions between a system and external actors (users or other systems).  Sequence diagrams, which are used to model interactions between system components, Dr. Noha Adly CSE 322 - System Modeling 14 14  12/23/2023 Use case modeling  A use case is a simple description of what a user expects from a system in that interaction  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.  Actors in a use case may be people or other systems.  Represented diagrammatically to provide an overview of the use case and in a more detailed textual form. Dr. Noha Adly CSE 322 - System Modeling 15 15  12/23/2023 Transfer-data use case  A use case in the Mentcare system representing the task of uploading data from the Mentcare to a more general Patient Record System  PRS is a more general system that maintains summary data about a patient rather than the data about each consultation, which is recorded in the Mentcare Actor 1 Actor 2 Dr. Noha Adly CSE 322 - System Modeling 16 16  12/23/2023 Tabular description of the ‘Transfer data’ use-case Use case diagrams give a simple overview of an interaction. So details must be added as either a simple textual description, a structured description in a table, or a sequence diagram Mentcare system: 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. Dr. Noha Adly CSE 322 - System Modeling 17 17  12/23/2023 Use cases in the Mentcare system involving the role ‘Medical Receptionist’ Dr. Noha Adly CSE 322 - System Modeling 18 18  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 19 19  12/23/2023 Sequence diagram for “View patient information” use case Dr. Noha Adly CSE 322 - System Modeling 20 20  12/23/2023 Sequence diagram for Transfer Data Dr. Noha Adly CSE 322 - System Modeling 21 21  12/23/2023 Structural models Dr. Noha Adly CSE 322 - System Modeling 22 22  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 23 23  12/23/2023 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.  focus here is on modeling of real-world objects as part of the requirements or early software design processes Dr. Noha Adly CSE 322 - System Modeling 24 24  12/23/2023 UML classes and association Dr. Noha Adly CSE 322 - System Modeling 25 25  12/23/2023 Classes and associations in the Mentcare Dr. Noha Adly CSE 322 - System Modeling 26 26  12/23/2023 The Consultation class Dr. Noha Adly CSE 322 - System Modeling 27 27  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 28 28  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 29 29  12/23/2023 A generalization hierarchy Dr. Noha Adly CSE 322 - System Modeling 30 30  12/23/2023 A generalization hierarchy with added detail Dr. Noha Adly CSE 322 - System Modeling 31 31  12/23/2023 Object class aggregation models  An aggregation model shows how classes that are collections are composed of other classes.  E.g. a study pack for a course may be composed of a book, PowerPoint slides, quizzes, recommendations for further reading.  Aggregation models are similar to the part-of relationship in semantic data models.  A patient record is a composition of Patient and an indefinite number of Consultations Dr. Noha Adly CSE 322 - System Modeling 32 32  12/23/2023 Behavioral models Dr. Noha Adly CSE 322 - System Modeling 33 33  12/23/2023 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. E.g. real time systems Dr. Noha Adly CSE 322 - System Modeling 34 34  12/23/2023 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.  For example, a phone billing system will accept information about calls made by a customer, calculate the costs of these calls, and generate a bill to be sent to that customer.  They are particularly useful during the analysis of requirements as they can be used to show end-to-end processing in a system. Dr. Noha Adly CSE 322 - System Modeling 35 35  12/23/2023 Data Flow model of the insulin pump’s operation using Activity model Dr. Noha Adly CSE 322 - System Modeling 36 36  12/23/2023 Order processing using sequence diagrams Sequence models highlight objects in a system, whereas data-flow diagrams highlight the functions. In practice non experts find dataflow more intuitive but engineers prefer sequence diagram Dr. Noha Adly CSE 322 - System Modeling 37 37  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 38 38  12/23/2023 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.  State charts are an integral part of the UML and are used to represent state machine models. Dr. Noha Adly CSE 322 - System Modeling 39 39  12/23/2023 State diagram of a microwave oven Dr. Noha Adly CSE 322 - System Modeling 40 40  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 41 41  12/23/2023 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. Dr. Noha Adly CSE 322 - System Modeling 42 42  12/23/2023 Model-driven engineering Dr. Noha Adly CSE 322 - System Modeling 43 43  12/23/2023 Model-Driven Engineering  Model-driven engineering (MDE) is an approach to software development where models rather than programs are the principal outputs of the development process.  The programs that execute on a hardware/software platform are then generated automatically from the models.  Proponents of MDE argue that this raises the level of abstraction in software engineering so that engineers no longer have to be concerned with programming language details or the specifics of execution platforms. Dr. Noha Adly CSE 322 - System Modeling 44 44  12/23/2023 Usage of model-driven engineering  Model-driven engineering is still at an early stage of development, and it is unclear whether or not it will have a significant effect on software engineering practice.  Pros  Allows systems to be considered at higher levels of abstraction  Generating code automatically means that it is cheaper to adapt systems to new platforms.  Cons  Models for abstraction are not necessarily right for implementation  Savings from generating code may be outweighed by the costs of developing translators for new platforms. Dr. Noha Adly CSE 322 - System Modeling 45 45