Download to read offline
Uploaded byvishal choudhary
SE-coupling and cohesion.ppt
High cohesion and low coupling are characteristics of good design that make software components more independent and modular. Cohesion refers to how related the responsibilities of a component are, while coupling refers to interdependencies between components. The document defines and provides examples of different types of cohesion and coupling, from ideal to poor, to help understand their impacts on maintenance and modifiability.
More Related Content
Similar to SE-coupling and cohesion.ppt
More from vishal choudhary
SE-coupling and cohesion.ppt
- 1.
- 2. Characteristics of GoodDesign • Component independence – High cohesion – Low coupling • Exception identification and handling • Fault prevention and fault tolerance
- 3. Coupling: Degree ofdependence among components No dependencies Loosely coupled-some dependencies Highly coupled-many dependencies High coupling makes modifying parts of the system difficult, e.g., modifying a component affects all the components to which the component is connected.
- 4. Range of Coupling HighCoupling Loose Low Content Common Control Stamp Data Uncoupled
- 5. Content coupling • Definition:One component references contents of another • Example: – Component directly modifies another’s data – Component refers to local data of another component in terms of numerical displacement – Component modifies another’s code, e.g., jumps into the middle of a routine
- 6. Example of ContentCoupling-1 Part of program handles lookup for customer. When customer not found, component adds customer by directly modifying the contents of the data structure containing customer data.
- 7. Example of ContentCoupling-2 Part of program handles lookup for customer. When customer not found, component adds customer by directly modifying the contents of the data structure containing customer data. Improvement: When customer not found, component calls the AddCustomer() method that is responsible for maintaining customer data.
- 8. Common Coupling • Definition:Two components share data – Global data structures – Common blocks • Usually a poor design choice because – Lack of clear responsibility for the data – Reduces readability – Difficult to determine all the components that affect a data element (reduces maintainability) – Difficult to reuse components – Reduces ability to control data accesses
- 9. Example-1 Each source processwrites directly to global data store. Each sink process reads directly from global data store. Process control component maintains current data about state of operation. Gets data from multiple sources. Supplies data to multiple sinks.
- 10. Example-2 Each source processwrites directly to global data store. Each sink process reads directly from global data store. Improvement Data manager component is responsible for data in data store. Processes send data to and request data from data manager. Process control component maintains current data about state of operation. Gets data from multiple sources. Supplies data to multiple sinks.
- 11. Control Coupling • Definition:Component passes control parameters to coupled components. • May be either good or bad, depending on situation. – Bad when component must be aware of internal structure and logic of another module – Good if parameters allow factoring and reuse of functionality
- 12. Example • Acceptable: Modulep calls module q and q passes back flag that says it cannot complete the task, then q is passing data • Not Acceptable: Module p calls module q and q passes back flag that says it cannot complete the task and, as a result, writes a specific message.
- 13. Stamp Coupling • Definition:Component passes a data structure to another component that does not have access to the entire structure. • Requires second component to know how to manipulate the data structure (e.g., needs to know about implementation) • May be necessary due to efficiency factors: this is a choice made by insightful designer, not lazy programmer.
- 14. Example-1 The print routineof the customer billing accepts a customer data structure as an argument, parses it, and prints the name, address, and billing information. Customer billing system
- 15. Example-2 The print routineof the customer billing accepts a customer data structure as an argument, parses it, and prints the name, address, and billing information. Improvement The print routine takes the customer name, address, and billing information as an argument. Customer Billing System
- 16. Data Coupling • Definition:Two components are data coupled if there are homogeneous data items. • Every argument is simple argument or data structure in which all elements are used • Good, if it can be achieved. • Easy to write contracts for this and modify component independently.
- 17. Key Idea inObject-Oriented Programming • Object-oriented designs tend to have low coupling.
- 18. Cohesion • Definition: Thedegree to which all elements of a component are directed towards a single task and all elements directed towards that task are contained in a single component. • Internal glue with which component is constructed • All elements of component are directed toward and essential for performing the same task • High is good
- 19. Range of Cohesion HighCohesion Low Functional Informational Sequential Communicational Procedural Temporal Logical Coincidental
- 20. Coincidental Cohesion • Definition:Parts of the component are only related by their location in source code • Elements needed to achieve some functionality are scattered throughout the system. • Accidental • Worst form
- 21. Example • Print nextline • Reverse string of characters in second argument • Add 7 to 5th argument • Convert 4th argument to float
- 22. Logical Cohesion • Definition:Elements of component are related logically and not functionally. • Several logically related elements are in the same component and one of the elements is selected by the client component.
- 23. Example-1 • A componentreads inputs from tape, disk, and network. All the code for these functions are in the same component. • Operations are related, but the functions are significantly different.
- 24. Example-2 • A componentreads inputs from tape, disk, and network. All the code for these functions are in the same component. Operations are related, but the functions are significantly different. Improvement • A device component has a read operation that is overridden by sub-class components. The tape sub-class reads from tape. The disk sub-class reads from disk. The network sub-class reads from the network.
- 25. Temporal Cohesion • Definition:Elements of a component are related by timing. • Difficult to change because you may have to look at numerous components when a change in a data structure is made. • Increases chances of regression fault • Component unlikely to be reusable.
- 26. Example-1 • A systeminitialization routine: this routine contains all of the code for initializing all of the parts of the system. Lots of different activities occur, all at init time.
- 27. Example-2 • A systeminitialization routine: this routine contains all of the code for initializing all of the parts of the system. Lots of different activities occur, all at init time. Improvement • A system initialization routine sends an initialization message to each component. • Each component initializes itself at component instantiation time.
- 28. Procedural Cohesion • Definition:Elements of a component are related only to ensure a particular order of execution. • Actions are still weakly connected and unlikely to be reusable
- 29. Example ... Read part numberfrom data base update repair record on maintenance file. ... • May be useful to abstract the intent of this sequence. Make the data base and repair record components handle reading and updating. Make component that handles more abstract operation.
- 30. Communicational Cohesion • Definition:Module performs a series of actions related by a sequence of steps to be followed by the product and all actions are performed on the same data
- 31. Example • Update recordin data base and send it to the printer. • database.Update (record). • record.Print().
- 32. Sequential Cohesion • Theoutput of one component is the input to another. • Occurs naturally in functional programming languages • Good situation
- 33. Informational Cohesion • Definition:Module performs a number of actions, each with its own entry point, with independent code for each action, all performed on the same data. • Different from logical cohesion – Each piece of code has single entry and single exit – In logical cohesion, actions of module intertwined • ADT and object-oriented paradigm promote
- 34. Functional Cohesion • Definition:Every essential element to a single computation is contained in the component. • Every element in the component is essential to the computation. • Ideal situation.
- 35. Examples of Cohesion-1 FunctionA Function B Function D Function C Function E Coincidental Parts unrelated Function A Function A’ Function A’’ logic Logical Similar functions Time t0 Time t0 + X Time t0 + 2X Temporal Related by time Function A Function B Function C Procedural Related by order of functions
- 36. Examples of Cohesion-2 FunctionA part 1 Function A part 2 Function A part 3 Functional Sequential with complete, related functions Function A Function B Function C Communicational Access same data Function A Function B Function C Sequential Output of one is input to another
- 37. Study • P1: Whatis the effect of cohesion on maintenance? • P2: What is the effect of coupling on maintenance? • P3: Produce an example of each type of cohesion. Justify your answers. • P4: Produce an example of each type of coupling. Justify your answers.