OO vs Structured Analysis Structured Analysis (still in use today) Divide and Conquer -At the function level Object-Oriented Analysis (still growing) Partition - At the level of concepts (objects)
Analysis 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.
Types of Software Real time software – E.g. control and monitoring systems – Must react immediately – Safety often a concern Data processing software – Used to run businesses – Accuracy and security of data are key Some software has both aspects
Requirements Document A system is a set of components that interact to solve a problem. System structure describes the systems objects and their interrelationships. System behavior describes how the system changes as its objects interact with one another. Every system has both structure and behaviordesigners must specify both.
Activities Common to Software Projects Design – Deciding how the requirements should be implemented, using the available technology – Includes: Systems engineering: Deciding what should be in hardware and what in software Software architecture: Dividing the system into subsystems and deciding how the subsystems will interact Detailed design of the internals of a subsystem User interface design Design of databases
Use Cases Use case diagrams are the starting point for UML-based software development
Conceptual models Must identify: Concepts, objects in our system, Associations between concepts: is part of, contains, manages, is-a, … Attributes of concepts Should not contain design information; e.g. methods. Better to over specify then under specify Concepts v/s attributes: when in doubt make it a concept Specification/Description concept: when keeping records
Interaction 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.
Interactions and messages – Show how a set of actors and objects communicate with each other to perform: The steps of a use case, or The 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 network These are all referred to as messages.
DFDs 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.
The DFD is an excellent communication tool for analysts to model processes and functional requirements Alone, however, it has limited usability. It is simple and easy to understand by users
Packages and importing A package combines related classes into subsystems – All the classes in a particular directory Classes in different packages can have the same name – Although not recommended Importing a package is done as follows: import finance.banking.accounts.*;
Key Concepts Abstraction – Object -> something in the world – Class -> objects – Superclass -> subclasses – Operation -> methods – Attributes and associations -> instance variables Modularity – Code can be constructed entirely of classes Encapsulation – Details can be hidden in classes – This gives rise to information hiding: Programmers do not need to know all the details of a class