COMP2007-Architectural patterns

Question 0

Model View Controller

Answer 0

Problem:
separation of UI from application

Context:
interactive applications with a flexible UI

Solution:
system model: UI (View and Controller component) decoupled from the application (Model component)

• components: collections of procedures (module)
• connectors: procedure calls
• control structure: single thread

Question 1

Definition

Answer 1

Describes a family of architectures in terms of their structural organisation.

Means of representing, sharing and reusing knowledge.

When uselful and when not

Can be represented using tabular and graphical descriptions.

Question 2

MVC - Model-View-Controller

Answer 2

Separates
presentation and
interaction from
system data.

Question 3

The model component

Answer 3

Manages system data and associated operations on that data.

Question 4

The view component

Answer 4

Defines and manages how the data is presented to the user.

Question 5

The controller component

Answer 5

manages user interaction and passes these to the view and the model.

Question 6

Mvc is used

Answer 6

When there are multiple ways to view and interact with the data

Also when future requirements for interaction and presentation of data are unknown.

Question 7

Advantages of MVC

Answer 7

Allows data to change independently of its representation and vice versa

Supports presentation of the same data in different ways with changes made in one representation shown in all of them.

Question 8

Disadvantages of MVC

Answer 8

Can involve additional code and code complexity when the data model and interactions are simple.

Question 9

Layered pattern

Answer 9

Problem
- distinct, hierarchical classes of services

Concentric circles of functionality

Question 10

Layered pattern context

Answer 10

A large system that requires decomposition (eg virtul machines, OSI model)

Question 11

Layered pattern solution

Answer 11

• system model:
  hierarchy of layers, often limited visibility
• components:
  collections of procedures (module)
• control structure: single or multiple threads

Question 12

Layered architecture

Answer 12

Used to model the interfacing of sub-systems

Organises the system into a set of layers (or abstract machines) each of which provide a set od services

…

Question 13

Layered architecture cont…

Answer 13

Supports incremental development of sub-systems in different layers

When a layer interface changes, only the adjacent layer is affected.

It is however, often artifici to structure systems in this way.

Question 14

Layered architecture pattern

Description

Answer 14

Organises the system into layers with related funtionality associated with each layer

A layer provides services to the layer above it so the lowest-lecel layers represent core services that are likely to be used throughout the system.

Question 15

Layered architectural pattern

When used

Answer 15

When building new fa ilities on top of existing systems;

when the development is spread accross several teams with each team responsible for a layer of functionality

when there is a requirement for multi-level security

Question 16

Layeres architecture pattern

Advantages

Answer 16

Allows replacement of entire layers so long as the interface is maintained

Redundant facilities can be provided in each layer to increase the dependability of the system

Question 17

Layered architecture pattern

Disadvantages

Answer 17

In practice difficult to provide a clean separation btwn layers

High level layer might have to interact directly with lower level rather than thru one between

Performance a prob cause od multiple levels of interpretation of a service requwst as it is processes at each layer.

Question 18

Repository pattern

Description

Answer 18

All data in system managed in a central repository accessible to all sys components which do not ibterCt directly, only through the repository.

Question 19

Repository pattern

Answer 19

.

Question 20

Repository pattern

Advantages

Answer 20

Components can be independent - they do not need to know of the e istence of other components.

Changes made by one component can be propagated to all components.

All data can be managed consistently (backups) as it is all in one place.

Question 21

Repository pattern

Disadvantages

Answer 21

As a single point of failure any probs can affect the whole system.

May be inefficiencies in organising all communication through the repository.

Distributing the repository across several computers may be difficult.

Question 22

Client server architecture

Description

Answer 22

Functionality of the system organised into services wirh each service delicered from a separate server. Clients are users of these services and access servers to make use of them.

Question 23

Client server architecture patern

When used

Answer 23

When data in a shared database has to be accessed from a range of locations. Because servers can be replicated, may also be used when the load on the sys is variable.

Question 24

Client server architecture pattern

Advantages

Answer 24

Servers can be distributed across a network.

General functionality (printing) can be a available to all clients and does not need to be implemented by all services.

Question 25

Client server architecture pattern

Disadvantages

Answer 25

Each service is a single point of failure so susceptible to denial of service attacks of server failure.

Performance may be unpredictable as it depends on the network as wekk as the system.

May be management problems if servers are owned by different organisations.

Question 26

Pipe and filter architecture pattern

Description

Answer 26

Processing of data in system is organised so tjat each processing component (filter) is discrete and carries out one type of data transformation.

The data flows (as in a pipe) from one component to another for processing.

Question 27

Pipe and filter architecture pattern

When used

Answer 27

In data processing applications where inputs are processed in separate stages to generate related outputs.

Question 28

Pipe and filter pattern

Advantages

Answer 28

Easy to understand and supports transformation reuse.

Workflow style matches the structure of many business processes.

Evolution by adding transformations is straightforward.

Can be implemented as either sequential or concurrent system.

Question 29

Pipe and filter architecture pattern

Disadvantages

Answer 29

Format for data transfer has to be agreed upon between communicating transformations.

Each transformation must parse its input and un-parse its output to the agreed form. This increases sys overhead and may mean its impossible to reuse functional transformations that use incompatible data structures.

Question 30

Architecture validation

Aim

Answer 30

Increase confidence of the design tem that the architecture is fit for purpose.

Has to be achieved within constraints of time and budget.

Be rigorous & efficient as poss.

Question 31

Architecture validation

Challenges

Answer 31

Design can’t be executed or tested.

May consist of new and COTS components that have to be integrated.

Question 32

Architecture validation

Techniques

Answer 32

Questioning; how does sys react to various situations; often make use of scenarios.

Construction of a prototype that creates a simple archetype of a desited application.

Measuring; quantitive measures, archit. metrics, simulation etc.

Identify potential flaws Nd improve b4 implementation.

Cheaper to fix before built