ARCHITECTURAL DESIGN
Design process to identifying sub-systems making up a system and the framework for sub-system control and communication.
Architectural Abstraction
Architecture in the small
Archtecture in the large
Advantages of Explicit Architecture
Stakeholder communication
System Analysis
Large scale reuse
The architecture may be reusable across a range of systems
Architecture may be used as a focus of discussion by system stakeholders
Analysis of whether the system can meet its no-functional requirements is possible.
Architecture and system characteristics
Performance
Security
Safety
Availability
Maintainabilty
4+1 view model
Architectural Patterns
Patterns are a means of representing, sharing and
reusing knowledge.
Stylized description of good design practice, which has been tried and tested in different environments
concerned with the way that an individual program is decomposed into components.
concerned with these enterprise systems are distiributed over different computers, which may be owned and managed by different companies
Use of architectural models
As a way of facilitating discussion about the system design
As a way of documenting an architecture that has been designed
Localise critical operations and minimise communications. Use large rather than fine-grain components.
Use a layered architecture with critical assets in the inner layers.
Localise safety-critical features in a small number of sub-systems.
Include redundant components and mechanisms for fault tolerance.
Use fine-grain, replaceable components
MVC Pattern
When used
Advantages
Disadvantages
Description
The Model component manages the system data and associated operations on that data.
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.
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
Can involve additional code and code complexity when the data model and interactions are simple.
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.
Layered architecture
Advantages
Disadvantages
When used
Example
Description
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.
A layered model of a system for sharing copyright documents held in different libraries
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 multi-level security.
Allows replacement of entire layers so long as the interface is maintained. Redundant facilities (e.g., authentication) can be provided in each layer to increase the dependability of the system.
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.
Repository architecture
Shared data is held in a central database or repository and may be accessed by all sub-systems;
Each sub-system maintains its own database and passes data explicitly to other sub-systems.
Repository Pattern
Description
When used
Advantages
Disadvantages
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.
When you have a system in which large volumes of information are generated that has to be stored for a long time. Also use it in data-driven systems where the inclusion of data in the repository triggers an action or tool.
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.
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.
The Client–server pattern
Description
When used
Advantages
Disadvantages
the functionality of the system is organized into services, with each service delivered from a separate server. Clients are users of these services and access servers to make use of them.
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.
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.
Each service is a single point of failure so susceptible to denial of service attacks or server failure. Performance may be unpredictable because it depends on the network as well as the system. May be management problems if servers are owned by different organizations.
Pipe and filter architecture
Description
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.
When used
Advantages
Disadvantages
Commonly used in data processing applications (both batch- and transaction-based) where inputs are processed in separate stages to generate related outputs.
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.
The format for data transfer has to be agreed upon 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 functional transformations that use incompatible data structures.
Application architectures
A generic application architecture is an architecture for a type of software system that may be configured and adapted to create a system that meets specific requirements.
Use of Application Architecture
As a way of organising the work of the development team.
As a means of assessing components for reuse.
As a design checklist.
As a vocabulary for talking about application types.
As a starting point for architectural design.
Examples of application types
Data processing applications
Transaction processing applications
Event processing systems
Language processing systems
Web-based information systems
Information and resource management systems are now usually web-based systems where the user interfaces are implemented using a web browser.