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Applications architecture is one of several architecture domains that form the pillars of an enterprise architecture or solution architecture. Note that the term "application architecture" (without the s) is commonly used for the internal structure of an application, for its software modularisation.
Applications architecture is the science and art of ensuring the suite of applications being used by an organization to create the composite architecture is scalable, reliable, available and manageable.
One not only needs to understand and manage the dynamics of the functionalities the composite architecture is implementing but also help formulate the deployment strategy and keep an eye out for technological risks that could jeopardize the growth and/or operations of the organization.
An application's architecture describes the structure and behavior of applications used in a business, focused on how they interact with each other and with users. It is focused on the data consumed and produced by applications rather than their internal structure. In application portfolio management, the applications are usually mapped to business functions and to application platform technologies.
The applications architecture is specified on the basis of business requirements. This involves defining the interaction between application packages, databases, and middleware systems in terms of functional coverage. This helps identify any integration problems or gaps in functional coverage. A migration plan can then be drawn up for systems which are at the end of the software life cycle or which have inherent technological risks.
Applications architecture means managing how multiple applications are poised to work together. It is different from software architecture, which deals with design concerns of one application.
 Applications architecture strategy
Strategy by definition is a stance and does not involve any action. Applications architecture strategy involves ensuring the applications and the integrations align with the growth strategy of the organization. If an organization is a manufacturing organization with fast growth plans through acquisitions, the applications architecture should be nimble enough to encompass inherited legacy systems as well as other large competing applications.
 Applications architecture patterns
Applications can be classified in various types depending on the applications architecture pattern they follow.
A "pattern" has been defined as: "an idea that has been useful in one practical context and will probably be useful in others”.
To create patterns, one needs building blocks. Building blocks are components of software, mostly reusable, which can be utilised to create certain functions. Patterns are a way of putting building blocks into context and describe how to use the building blocks to address one or multiple architectural concerns.
An application is a compilation of various functionalities, all typically following the same pattern. This pattern defines the application’s pattern.
Applications typically follow one of the following industry-standard applications architecture patterns:
- Client-Proxy Server: Acts as a concentrator for many low-speed links to access a server.
- Customer Support: Supports complex customer contact across multiple organisations.
- Reactor: Decouples an event from its processing.
- Replicated Servers: Replicates servers to reduce burden on central server.
- Layered Architecture: A decomposition of services such that most interactions occur only between neighboring layers.
- Pipe and Filter Architecture: Transforms information in a series of incremental steps or processes.
- Subsystem Interface: Manages the dependencies between cohesive groups of functions (subsystems).
- Self-Service: Users accessing transactions on a 24x7 basis (a.k.a. user-to-business)
- Collaboration: Users working with one another to share data and information (a.k.a. user-to-user)
- Information Aggregation: Data from multiple sources aggregated and presented across multiple channels (a.k.a. user-to-data)
- Event-Centric: Data events (which may have initially originated from a device, application, user, data store or clock) and event detection logic which may conditionally discard the event, initiate an event-related process, alert a user or device manager, or update a data store.
- Enterprise Process-Centric: A business process manages the interactions between multiple intra-enterprise applications, services, sub-processes and users.
- Bulk Processing: A business process manages the interactions between one or more bulk data sources and targets.
- Extended Enterprise: A business process manages the interactions between multiple inter-enterprise applications, services, sub-processes and users.
The right applications pattern depends on the organisation's industry and use of the component applications. An organisation could have a mix of multiple patterns if it has grown both organically and through acquisitions...
 Tasks of an applications architect
An applications architect is a master of everything application-specific in an organization. An applications architect provides strategic guidelines to the applications maintenance teams by understanding all the applications from the following perspectives
- Interoperability capability
- Performance and scalability
- Reliability and availability
- Application lifecycle stage
- Technological risks
- Number of instances
The above analysis will point out applications that need a range of changes – from change in deployment strategy for fragmented applications to a total replacement for applications at the end of their technology or functionality lifecycle.
 Functionality footprint
Understand the system process flow of the primary business processes. It gives a clear picture of the functionality map and the applications footprint of various applications across the map.
Many organizations do not have documentation discipline and hence lack detailed business process flows and system process flows. One may have to start an initiative to put those in place first.
 Create solution architecture guidelines
Every organization has a core set of applications that are used across multiple divisions either as a single instance or a different instance per division. Create a solution architecture template for all the core applications so that all the projects have a common starting ground for designing implementations.
The standard of today Architecture world is TOGAF, driven by The Open Group Architecture Framework. It covers all components of EA, including Application as well as Technology Architecture
There are also other Standards to consider, depending on the level of complexity of the organization.
The Zachman Framework for Enterprise Architectures, Federal Enterprise Architecture (FEA) & Gartner.
For references and basic understanding check IEEE Standard 1471-2000: IEEE Recommended Practice for Architectural Description of Software-Intensive Systems I