ObjectOriented Software Engineering CIS 375 Bruce R Maxim

Object-Oriented Software Engineering CIS 375 Bruce R. Maxim UM-Dearborn 1

OO Concepts - 1 • Object – encapsulates both data (attributes) and data manipulation functions (called methods, operations, and services) • Class – generalized description (template or pattern) that describes a collection of similar objects • Superclass – a collection of objects • Subclass – an instance of a class 2

OO Concepts - 2 • Class hierarchy – attributes and methods of a superclass are inherited by its subclasses • Messages – the means by which objects exchange information with one another • Inheritance – provides a means for allowing subclasses to reuse existing superclass data and procedures – provides mechanism for propagating changes 3

OO Concepts - 3 • Polymorphism – mechanism that allows several objects in an class hierarchy to have different methods with the same name – instances of each subclass will be free to respond to messages by calling their own version of the method 4

Advantages of OO Architectures • Implementation details of data and procedures hidden from the outside world – reduces propagation of side effects after changes • Data structures and operators are merged in single entity or class – this facilitates reuse • Interfaces among encapsulated objects are simplified – reduces system coupling 5

Class Construction Options - 1 • Build new class from scratch without using inheritance • Use inheritance to create new class from existing class contains most of the desired attributes and operations • Restructure the class hierarchy so that the required attributes and operations can be inherited by the newly created class 6

Class Construction Options - 2 • Override some attributes or operations in an existing class and use inheritance to create a new class with (specialized) private versions of these attributes and operations. 7

Object-Oriented Evolutionary Process Model • • • Customer communication Planning Risk analysis Engineering construction and analysis Customer evaluation 8

Object-Oriented Software Construction • • Identify candidate classes Look-up classes in library Extract classes if available Engineer classes if not available – – Object-oriented analysis (OOA) Object-oriented design (OOD) Object-oriented programming (OOP) Object-oriented testing (OOT) • Put new classes in library • Construct Nth iteration of the system 9

Class Candidates • External Entities – devices or people • Things in Problem Domain – Reports, displays, signals • Events – completion of some task • Roles – manager, engineer, salesperson • Organizational Units – divisions, groups, teams • Structures – sensors, vehicles, computers 10

Criteria for Including Objects • Does object information need to be retained? • Does object provide a set of needed services that can change its attributes? • Does object have major (important) attributes? • Can you identify common attributes for all object instances? • Can you identify common operations for all object instances? • Is it an external entity that produces or consumes information? 11

Object-Oriented Life Cycle Model 12

Management of OO Projects • Establish a common process framework (CPF). • Use CPF & historic data to eliminate time & effort. • Specify products & milestones. • Define Q. A. checkpoints. • Manage changes. • Monitor project. 13

OO Project Milestones • • • Contracts completed. OO Analysis completed. OO Design completed. OO Programming completed. OO Testing completed. 14

OO Project Metrics • • • Number of scenario scripts. Number of key classes. Number of support classes. (# key classes)/(# support classes). Number of major iterations (around spiral model). • Number of completed contracts. 15

OO Estimation - 1 1. Use some effort decomposition technique (e. g. FP) to determine size estimates. 2. Use O. O. A. to develop scenario scripts and count them. 3. Use O. O. A. to get the number of key classes. 4. Categorize types of the user interfaces to determine support class multiplier: No. UI = 2. 0 Text. UI = 2. 25 GUI = 2. 5 Complex GUI = 3. 0 16

OO Estimation - 2 5. Estimate the number of support classes # support classes = (# of key classes) * (UI #) 6. Estimate total effort Total effort = (key + support) * (average # of work units per class) 7. Cross check class based estimate (6) using Total effort = (avg. # of work units per script) * (# of scenario scripts) Note: takes 15 -20 days to complete each class. 17