The authors of book "Design patterns" are known as "Gang of Four" :
Saturday, 25 June 2016
What is the GRASP principle ?
General Responsibility Assignment Software Principles
- Guidelines for assigning responsibility to classes and objects in OO design.
- uses various patterns :
- Controller
- A non-user interface object responsible for receiving or handling a system event.
- Creator
- Factory Pattern (GoF)
- Indirection
- Proxy Pattern (GoF)
- Information Expert
- Information Hiding
- High Cohesion
- Low Coupling
- Polymorphism
- Protected Variations
- Open Close Principle of SOLID principle
- Pure Fabrication
- System as a set of related software functionalities that can be reused for different purposes
'IS A' vs. 'HAS A'
has-a
- A composition relationship where one object "belongs to" another object and behaves according to the rules of ownership.
is-a
- A relationship between abstractions (e.g. types, classes), where one class A is a subclass of another class B
Favor Composition over inheritance
What are the Software Design considerations ?
Software Design considerations
- Compatibility
- Extensibility
- Fault-tolerance
- Maintainability
- Modularity
- Reliability
- Reusability
- Robustness
- Security
- Usability
- Performance
- Portability
- Scalability
- Availability
- Recoverability
- Monitorability
What are the principles of Software Design ?
Software design principles
- SOLID
- GRASP
- DRY (Don’t Repeat Yourself)
- KISS (Keep It Simple and Stupid)
- YAGNI (You Aren’t Gonna Need It)
- If it ain’t broken, don’t fix it !
What are the common practices for improving SLRs ?
Redundancy
- Load Balancing
- Failover
- Clustering
Availability
- Active replication : performed by processing the same request at every replica
- Passive replication : involves processing each single request on a single replica and then transferring its resultant state to the other replicas
Performance
- Increase system capacity
- Increase computational efficiency
Extensibility
- Clearly define the scope in the service-level agreement
- Anticipate expected changes
- Design a high-quality object model
Scalability
- Vertical Scalability : more processors, memory, and disks
- Horizontal Scalability : more servers
Reliability
- Increase computational efficiency
- Transactions
- Monitor and restart
- Redundancy
- Degradation
- Bound execution time
What is the impact of dimensions on SLRs (Service level requirements) ?
Capacity
- Raw power in an element - CPU, fast network connection, or large storage capacity
- increased through vertical scaling
- can improve performance, availability, and scalability
Redundancy
- Multiple systems that work on the same job - Load balacing
- increased through horizontal scaling
- can increase performance, reliability, availability, extensibility, and scalability
- can decrease manageability and security
Modularity
- Dividing a computational problem into separate elements
- can increase scalability, extensibility, maintainability, and security
- can decrease performance, reliability, availability, and manageability
Tolerance
- Time available to fulfill a request from a user
- can increase performance, scalability, reliability, and manageability
Workload
- Computational work being performed at a particular point within the system
- consumes available Capacity
- can increase performance, scalability, and availability
Heterogeneity
- Diversity in technologies that is used within a system
- can increase performance and scalability
- can decrease performance, scalability, availability, extensibility, manageability, and security
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