Software Lifecycle Activities

Software Lifecycle Activities
Requirements Elicitation Requirements Analysis System Design Object Design Implemen- tation Testing Use Case Model Verified By Implemented By Realized By Structured By Expressed in Terms Of Application Domain Objects SubSystems Implementation Domain Objects class... Source Code Test Cases ? class.... April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

From Use Cases to Objects
Le v el 1 Level 1 Use Case Le v el 2 Le v el 2 Level 2 Use Cases Le v el 3 Le v el 3 Le v el 3 Level 3 Use Cases Le v el 4 Le v el 4 Operations A B Participating Objects April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Definition: Object Modeling
Main goal: Find the important abstractions What happens if we find the wrong abstractions? Iterate and correct the model Steps during object modeling: 1. Class identification (based on the fundamental assumption that we can find abstractions) 2. Find the attributes 3. Find the methods 4. Find the associations between classes (Order of steps is secondary, only a heuristic) April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Do UML associations have direction?
An association between two classes is by default a bi-directional mapping. A B Class A can access class B and class B can access class A Both classes play the agent role. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Do UML associations have direction?
If you want to to make A a client, and B a server, you can make the association unidirectional. The arrowhead points to the server role: A B access  Class A ( the “client”) accesses class B (“the server”). B is also called navigable April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

CS410 – Software Engineering Lecture #10: UML II/Testing
Aggregation Models "part of" hierarchy Useful for modeling the breakdown of a product into its component parts (sometimes called bill of materials (BOM) by manufacturers) UML notation: Like an association but with a small diamond indicating the assembly end of the relationship. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Aggregation weight Automobile serial number year manufacturer model color drive purchase Engine horsepower volume on off Battery amps volts charge discharge 3,4 Wheel diameter number of bolts 2 Brakelight on off 2,4 Door open close April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Inheritance Models "kind of" hierarchy Powerful notation for sharing similarities among classes while preserving their differences UML Notation: An arrow with a triangle Cell NerveCell BloodCell MuscleCell Red White Smooth Striate Cortical Pyramidal April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Aggregation vs. Inheritance
Both associations describe trees (hierarchies). Aggregation tree describes “part-of” relationships (also called and-relationship) Inheritance tree describes "kind-of" relationships (also called or-relationship) Aggregation relates instances (involves two or more different objects) Inheritance relates classes (a way to structure the description of a single object) April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Other Associations “Uses”: A subsystem uses another subsystem (System Design) “Contains”: Sometimes called “spatial aggregation” ... contains ... Example: A UML package contains another UML package Parent/child relationship: ... is father of ... ... is mother of ... Seniority: ... is older than ... ... is more experienced than ... April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Object Types Entity Objects: Represent the persistent information tracked by the system (Application domain objects, “Business objects”) Boundary Objects: Represent the interaction between the user and the system Control Objects: Represent the control tasks performed by the system April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Roles A role name is the name that uniquely identifies one end of an association. A role name is written next to the association line near the class that plays the role. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Roles When do you use role names? Necessary for associations between two objects of the same class Also useful to distinguish between two associations between the same pair of classes When do you not use role names? If there is only a single association between a pair of distinct classes, the names of the classes serve as good role names April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Example of Role Problem Statement: A person assumes the role of repairer with respect to another person, who assumes the role of inspector with respect to the first person. Person Creates Workorders Person inspector repairperson April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Roles in Associations Client Role: An object that can operate upon other objects but that is never operated upon by other objects. Server Role: An object that never operates upon other objects. It is only operated upon by other objects. Agent Role: An object that can both operate upon other objects and be operated upon by other objects. An agent is usually created to do some work on behalf of an actor or another agent. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Qualification The qualifier improves the information about the multiplicity of the association between the classes. It is used for reducing 1-to-many multiplicity to 1-1 multiplicity. Example: Without qualification, a directory has many files. A file belongs to only one directory. File filename 1 * Directory Directory filename 0..1 1 File With qualification: A directory has many files, each with a unique name. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Software Lifecycle Activities
Requirements Elicitation Requirements Analysis System Design Object Design Implemen- tation Testing Use Case Model Verified By Implemented By Realized By Structured By Expressed in Terms Of Application Domain Objects SubSystems Implementation Domain Objects class... Source Code Test Cases ? class.... April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

What is this? April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Erroneous State (“Error”)
April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Algorithmic Fault April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Mechanical Fault April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Examples of Faults and Errors
Faults in the Interface specification Mismatch between what the client needs and what the server offers Mismatch between requirements and implementation Algorithmic Faults Missing initialization Branching errors (too soon, too late) Missing test for nil Mechanical Faults (very hard to find) Documentation does not match actual conditions or operating procedures Errors Stress or overload errors Capacity or boundary errors Timing errors Throughput or performance errors April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

How do we deal with errors and faults?

Verification? April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Modular Redundancy? April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Declaring the Bug as a Feature?

Patching? April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Dealing with Errors Verification: Assumes hypothetical environment that does not match real environment Proof might be buggy (omits important constraints; simply wrong) Modular redundancy: Expensive Declaring a bug to be a “feature” Bad practice Patching Slows down performance Testing (this lecture) Testing is never good enough April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Another View on How to Deal with Errors
Error prevention (before the system is released): Use good programming methodology to reduce complexity Use version control to prevent inconsistent system Apply verification to prevent algorithmic bugs Error detection (while system is running): Testing: Create failures in a planned way Debugging: Start with unplanned failures Monitoring: Deliver information about state. Find performance bugs Error recovery (recover from failure once the system is released): Modular redundancy Recovery blocks April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Some Observations It is impossible to completely test any nontrivial module or any system. Theoretical limitations: Halting problem Practical limitations: Prohibitive in time and cost Testing can only show the presence of bugs, not their absence (Dijkstra). April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Testing Takes Creativity
Testing often viewed as dirty work. To develop an effective test, one must have: Detailed understanding of the system Knowledge of the testing techniques Skill to apply these techniques in an effective and efficient manner Testing is done best by independent testers. We often develop a certain mental attitude that the program should behave in a certain way when in fact it does not. Programmers often stick to the data set that makes the program work. "Don’t mess up my code!" A program often does not work when tried by somebody else. Don't let this be the end-user. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Fault Handling Techniques
Fault Avoidance Fault Detection Fault Tolerance Design Methodology Verification Reviews Configuration Management Testing Debugging Modular Redundancy Component Testing Integration Testing System Testing Correctness Debugging Performance Debugging April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Component Testing Unit Testing: Individual subsystem Carried out by developers Goal: Confirm that subsystem is correctly coded and carries out the intended functionality Integration Testing: Groups of subsystems (collection of classes) and eventually the entire system Goal: Test the interfaces among the subsystems April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

System Testing System Testing: The entire system is tested Carried out by developers Goal: Determine if the system meets the requirements (functional and global) Acceptance Testing: Evaluates the system delivered by developers Carried out by the client. May involve executing typical transactions on site on a trial basis Goal: Demonstrate that the system meets customer requirements and is ready to use Implementation (Coding) and testing go hand in hand. April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

Unit Testing Informal: Incremental coding Static Analysis: Hand execution: Reading the source code Walk-Through (informal presentation to others) Code Inspection (formal presentation to others) Automated Tools checking for syntactic and semantic errors departure from coding standards Dynamic Analysis: Black-box testing (Test the input/output behavior) White-box testing (Test the internal logic of the subsystem or object) Data-structure based testing (Data types determine test cases) April 4, 2019 CS410 – Software Engineering Lecture #10: UML II/Testing

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