Architectural patterns

Question 1

Describe MVC pattern.

Answer 1

Separates presentation and interaction from the system data. The system is structured into three logical components that interact with
each other. The Model component manages the system data and associated operations on that data. The View component defines and
manages how the data is presented to the user. The Controller component manages user interaction (e.g., key presses, mouse clicks, etc.) and passes these interactions to the View and the Model.

Question 2

When is MVC used?

Answer 2

Used when there are multiple ways to view and interact with data. Also used when the future requirements for interaction and
presentation of data are unknown.

Question 3

What are the advantages of MVC?

Answer 3

Allows the 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 4

What are the disadvantages of MVC?

Answer 4

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

Question 5

Describe Layered architecture pattern.

Answer 5

Organizes the system into layers, with related functionality associated with each layer. A layer provides services to the layer above it, so the lowest level layers represent core services that are likely to be used throughout the system.

Question 6

When is layered architecture used?

Answer 6

Used when building new facilities on top of existing systems; when the development is
spread across several teams with each team responsibility for a layer of functionality; when
there is a requirement for multilevel security.

Question 7

What are the advantages of layered architecture?

Answer 7

Allows replacement of entire layers as long as the interface is maintained. Redundant facilities
(e.g., authentication) can be provided in each layer to increase the dependability of the system.

Question 8

What are the disadvantages of layered architecture?

Answer 8

In practice, providing a clean separation between layers is often difficult, and a high-level layer may have to interact directly with lower-level layers rather than through the layer immediately below it. Performance can be a problem because of multiple levels of interpretation of a service request as it is processed at each layer.

Question 9

Describe repository pattern.

Answer 9

All data in a system is managed in a central repository that is accessible to all system
components. Components do not interact directly, only through the repository.

Question 10

When is repository architecture used?

Answer 10

You should use this pattern when you have a system in which large volumes of information are generated that has to be stored for a long time. You may also use it in data-driven systems where the inclusion of data in the repository triggers an action or tool.

Question 11

What are the advantages of repository architecture?

Answer 11

Components can be independent; they do not need to know of the existence of other
components. Changes made by one component can be propagated to all components. All data can be managed consistently (e.g., backups done at the same time) as it is all in one place.

Question 12

What are the disadvantages of repository architecture?

Answer 12

The repository is a single point of failure so problems in the repository affect the whole
system. May be inefficiencies in organizing all communication through the repository.
Distributing the repository across several computers may be difficult.

Question 13

Describe client-server pattern

Answer 13

In a client–server architecture, the system is presented as a set of services, with each service delivered by a separate server. Clients are users of these services and access servers to make
use of them.

Question 14

When is client-server architecture used?

Answer 14

Used 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 a system is variable.

Question 15

What are the advantages of client-server architecture?

Answer 15

The principal advantage of this model is that servers can be distributed across a network. General functionality (e.g., a printing service) can be available to all clients and does not
need to be implemented by all services.

Question 16

What are the disadvantages of client-server architecture?

Answer 16

Each service is a single point of failure and so is susceptible to denial-of-service attacks or server failure. Performance may be unpredictable because it depends on the network as well as the system. Management problems may arise if servers are owned by different organizations.

Question 17

Describe pipe and filter pattern

Answer 17

The processing of the data in a system is organized so that 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 18

When is pipe and filter used?

Answer 18

Commonly used in data-processing applications (both batch and transaction-based) where inputs are processed in separate stages to generate related outputs.

Question 19

What are the advantages of pipe and filter?

Answer 19

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 a sequential or concurrent system.

Question 20

What are the disadvantages of pipe and filter?

Answer 20

The format for data transfer has to be agreed between communicating transformations. Each transformation must parse its input and unparse its output to the agreed form. This
increases system overhead and may mean that it is impossible to reuse architectural components that use incompatible data structures.