CS504 Final Term Short Notes Set 2

CS504 Short Notes

Lecture 22

What is Software architecture?

It provides an over all view of a high level system.

In it, we define how a system is decomposed into sub systems, components modules and relationship among those components and subsystems etc.

What is the importance of software architecture?

It serves as a mean of communication between the stack holders.

Helps in making early design decisions.

Reusability is achieved.

Attributes of software architecture address both functional and non functional requirements of a software system. These attributes are as under:

Performance

by localizing the operations to minimize the communication between subsystems.

Security

by adopting a layered architecture.

Safety by isolating a specific/safety critical components.

Availability by building redundancy i.e. by providing suitable alternatives in case of an expected or unexpected system failure.

Maintainability

by using self contained components i.e. change in a component should not bring a change in another component.

Lecture 23

A software Architecture usually consists of the following elements which are presented in a model below : Logical view/Functionl view comprises of various different functions provided by the system abstraction and the domain elements.

Development View

Comprises of the different files and directories in the system.

Code view Comprises of classes, objects, procedures function, subsystems, layers and modules.

Concurrency View

Documents different parallel processes and threads in the system having its main focus on even synchronization and parallel data flow.

Physical view

Depicts how a system would physically be deployed.

Architectural styles may describe i) A set of components that perform a function required by a system. ii) A set of connectors that enable communication among components iii) Integrating components from the system and semantic models that enable a designer to understand the over properties of a system.

what is control modelling?

Architectural design process consists of three activities; System structure, modular decomposition and control modeling. These three activities are performed to design architecture of a system. In system structuring, we divide system into major blocks (sub systems). In modular decomposition, these sub-systems or blocks are further decomposed into modules. These modules should be connected in term of control flow to make system executable. This is done through control modeling. In control modeling, we model flow of control among different modules of the system to enable different sub-systems to communicate and for working as a single system.

In client server model why server does not need to know about clients? please explain Normally the total no. of servers in a organization remain fix whereas the clients go on increasing and decreasing. If we implement the system in a way, where server doesn’t know about the clients, then this gives us the flexibility to add/delete clients easily. In this case adding a client mean just connect the client with the server and start using the services. Also in most of the cases server don't need to know about the clients, so keeping record of clients may be burden especially in case when the clients increase significantly.

Lecture 24

Architectural Styles:

Data centered shared data is held in a centeral data base or each subsystem maintains its own database.

Client server model

a distributed system model which describes how data and processing is distributed across a range of components. Application is modeled as set of services provided by the servers and a set of clients that use these services. Clients know the servers but the servers do not need to know all the clients. Mapping between processors is also not always 1:1.

Server types, File servers, Data base servers, Transaction servers, Groupware servers.

Server Configuration:

Thing client Model Client machine has no functionality on it. It just provides the user interface.

Fat client Model

more processing is delegated to the client as the application processing is locally extended. concept of architectural views, specialy logical view please sir elaborate it in simple words and it is also request that define it with the help of any real life example.???

Please note that an architectural views represent the viewpoints of different stakeholders. That is a view presents system from one angel, other view presents system from another angel and so on. eg, just as a building architect might create wiring diagrams, floor plans, and elevations to describe different facets of a building to its different stakeholders (electricians, owners, planning officials), so an IT architect might create logical view, implementation view and so on.

In logical view, architect presents the system from end user point of view that what functionality and services the system provides. It describes how the system is structured in terms of units of implementation. Normally this view includes class diagram, communication diagram, sequence diagrams etc. An Architecture style is a set of principles which you can use to build a system, normally these principals are re-used in applications, e.g. client/server architectural style, component based, layered etc etc. each of which provides a way to implement software structure.

Non functional requirements are qualities and characteristics of a system. They define the criteria to judge the operation of the system. e.g. system must be maintainable, system must be secure, system must be user friendly etc.