4OO vs Structured Analysis ♦Structured Analysis (still in use today)−Divide and ConquerAt the function level♦Object-Oriented Analysis (still growing)−Partition- At the level of concepts (objects)
5Analysis vs Design Analysis stage: - focus on high-level specification that- Describes what the system is supposed to do.Design specification:- focus on how the system should be constructed to satisfy these requirements.
6Types of Software Real time software Data processing software E.g. control and monitoring systemsMust react immediatelySafety often a concernData processing softwareUsed to run businessesAccuracy and security of data are keySome software has both aspects
7Requirements Document A system is a set of components that interact to solve a problem.System structure describes the system’s objects and their interrelationships.System behavior describes how the system changes as its objects interact with one another.Every system has both structure and behavior—designers must specify both.
9Activities Common to Software Projects DesignDeciding how the requirements should be implemented, using the available technologyIncludes:Systems engineering: Deciding what should be in hardware and what in softwareSoftware architecture: Dividing the system into subsystems and deciding how the subsystems will interactDetailed design of the internals of a subsystemUser interface designDesign of databases
11Use CasesUse case diagrams are the starting point for UML-based software development
12Conceptual models Must identify: Concepts, objects in our system,Associations between concepts: is part of, contains, manages, is-a, …Attributes of conceptsShould not contain design information; e.g. methods.Better to over specify then under specifyConcepts v/s attributes: when in doubt make it a conceptSpecification/Description concept: when keeping records
14Interaction diagrams Model the dynamic aspects of a software system Visualize how the system runs.Built from a use case and a class diagram.Show how a set of objects accomplish the required interactions with an actor.
16Interactions and messages Show how a set of actors and objects communicate with each other to perform:The steps of a use case, orThe steps of some other piece of functionality.The set of steps, taken together, is called an interaction.Can show several different types of communication.E.g. method calls, messages send over the networkThese are all referred to as messages.
24DFDs OR Activity Diagrams Squares representing external entities, which are sources or destinations of data.Rounded rectangles representing processes, which take data as input, do something to it, and output it.Arrows representing the data flows, which can either be electronic data or physical items.Open-ended rectangles representing data stores, including electronic stores such as databases or XML files and physical stores such as or filing cabinets or stacks of paper.
25The DFD is an excellent communication tool for analysts to model processes and functional requirementsAlone, however, it has limited usability. It is simple and easy to understand by users
31Packages and importing A package combines related classes into subsystemsAll the classes in a particular directoryClasses in different packages can have the same nameAlthough not recommendedImporting a package is done as follows:import finance.banking.accounts.*;
32Key Concepts Abstraction Object -> something in the world Class -> objectsSuperclass -> subclassesOperation -> methodsAttributes and associations -> instance variablesModularityCode can be constructed entirely of classesEncapsulationDetails can be hidden in classesThis gives rise to information hiding:Programmers do not need to know all the details of a class