What is application architecture?
Application architecture is the part of enterprise architecture that describes which applications an organisation has, which functions and data they provide, how they connect to each other and to business processes, and how that landscape should evolve over time. It links business architecture, which defines what the organisation needs to be able to do, with technical architecture, which provides the servers, networks and cloud services on which software runs. In an industrial setting it also covers OT applications such as SCADA, historians and MES, which are increasingly connected to office systems.
Application architecture translates business needs into a coherent, manageable software landscape.
🧠 What does an application architecture cover?
An application architecture is not a list of programs but a model of components and their relationships. Its main building blocks are:
| Component | Description | Typical artefact |
|---|---|---|
| Application landscape | Overview of all applications and their functions | Landscape map, application portfolio |
| Interfaces and integrations | How applications exchange data (APIs, messages, files, ESB) | Interface catalogue, integration diagram |
| Application functions and services | What each application contributes to processes or users | Function-to-application matrix |
| Data objects | Which data an application creates, reads or manages, and which system is the source | CRUD matrix, data source overview |
| User groups | Which departments or roles use which application | Role-to-application matrix |
| Lifecycle status | Being implemented, in use, being phased out, being replaced | Roadmap, lifecycle management |
The modelling language ArchiMate (version 3.2, October 2022) has dedicated application layer elements: the application component (a modular, replaceable piece of software that encapsulates behaviour and data), the application interface, the application collaboration, behaviour elements such as application function, process, event and service, and the passive data object. Using these elements consistently makes landscape maps comparable across departments and organisations.
🔁 How does application architecture relate to the other layers?
| Architecture layer | Link with application architecture |
|---|---|
| Business Architecture | Determines which processes, functions and services need support |
| Information Architecture | Defines which data is needed, which system is the source and who owns it |
| Application architecture | Assigns functions and data to concrete applications and interfaces |
| Technical Architecture | Provides the infrastructure applications run on: servers, networks, storage, cloud |
In TOGAF (the 10th Edition was released in April 2022), application architecture belongs to Phase C of the Architecture Development Method, Information Systems Architectures. That phase combines data and application architecture, in either order. The steps are always the same: select reference models and viewpoints, describe the current state (baseline), design the desired state (target), perform a gap analysis and derive candidate roadmap components from it.
A well-designed application architecture prevents duplicated functionality, fragmentation and unwanted vendor lock-in. A well-known rule of thumb is Conway’s law (1968): systems tend to mirror the communication structure of the organisation that builds them. Organisations that keep IT and OT apart organisationally often end up with separate, poorly connected application landscapes as well.
🏛 How does Dutch government use application architecture?
Dutch government bodies work with reference architectures that fall under NORA. Each fills in the application layer in its own way:
| Architecture | Role of application architecture |
|---|---|
| NORA | Principles and generic functions for all of government, such as reuse and open standards |
| GEMMA | Reference components for municipal applications, the Softwarecatalogus and Common Ground (data kept at the source and exposed via APIs) |
| WILMA | Applications for water management, permits, enforcement, reports and asset management at the 21 water boards |
| MARIJ | Historic central government architecture for ministries and executive agencies, later succeeded by EAR and RORA |
Typical application types in such a landscape include a case management system (case-based working using the RGBZ data model), a document management system (DMS) or records management application (RMA) for archiving and version control, HR and finance systems, portals for citizens and businesses and, at water boards and drinking water companies, SCADA and HMI software.
National agreements apply to integrations. Digikoppeling has been on the ‘comply or explain’ list of the Dutch Standardisation Forum since 2009 and has profiles for synchronous requests (WUS), reliable asynchronous messaging (ebMS), large messages and REST APIs. The REST API Design Rules (version 2.2) are also mandatory under ‘comply or explain’ whenever government organisations, including municipalities and water boards, offer a REST API.
🏭 What does application architecture look like in an OT environment?
In operational technology (OT), applications are often embedded or highly specialised, but they still belong in the application landscape. The ISA-95 model and the Purdue Model help to organise them by level:
| Level | OT or IT application | Function |
|---|---|---|
| 4 – Business planning | ERP, planning, maintenance and asset management | Orders, inventory, finance, work orders, calibrations |
| 3 – Manufacturing operations | MES, historian, LIMS | Production orders, traceability, time series, quality |
| 2 – Supervisory | SCADA, HMI, alarm management | Monitoring and operating the process |
| 1 – Control | PLC and DCS software | Real-time control and interlocks |
| Cross-cutting | edge computing, Unified Namespace, IT/OT integration platforms | Local processing and data distribution across levels and to ERP and BI systems |
Three differences from office applications drive the design choices:
- Lifespan - a control or SCADA application often runs for fifteen to twenty years or more, so legacy systems are normal and replacement has to be planned around maintenance shutdowns.
- Availability over confidentiality - an integration must never disrupt process control; changes go through strict change management.
- Standardised integration - OPC UA and MQTT increasingly replace proprietary protocols and point-to-point links. In the process industry, NAMUR Open Architecture adds a separate second channel, in principle one-way, for monitoring and optimisation.
An application architecture for OT must therefore include security: which application sits in which zone and through which conduit it communicates, as IEC 62443-3-2 requires, and how network segmentation limits integrations between IT and OT. See also OT Architecture for the wider structure of networks and systems.
🔧 How do you build an application architecture step by step?
- Take inventory - record every application with its owner, supplier, version, users and interfaces. A CMDB or an OT asset inventory is a good starting point, but often lacks the functional view.
- Map to functions and processes - build a matrix of business functions against applications. Duplicates and gaps become visible immediately.
- Map data flows - for each data object, decide which application is the source and which systems consume it.
- Assess the portfolio - many organisations use Gartner’s TIME model, which scores each application on business value and technical fit:
| TIME quadrant | Business value | Technical fit | Action |
|---|---|---|---|
| Tolerate | Low | High | Keep running, invest minimally |
| Invest | High | High | Develop and extend |
| Migrate | High | Low | Move the functionality to a new platform |
| Eliminate | Low | Low | Phase out and archive the data |
- Design the target architecture - choose principles, standards and an integration pattern (for example API-led, a message bus or a Unified Namespace).
- Plan the migration - turn the gap analysis into a roadmap with projects, dependencies and maintenance windows.
- Keep it current - maintain the model through architecture reviews for every new purchase or change.
🧩 Which architecture principles apply to applications?
- Reuse generic functions - build or buy a function once and let several processes use it.
- Minimise dependencies - loose coupling through documented interfaces instead of direct database links.
- Use open standards - for example REST and JSON, Digikoppeling in Dutch government and OPC UA in industry.
- Keep data at the source - store data once and expose it, rather than copying it into every package.
- Avoid duplicate functionality - one application per function, unless there is a good reason.
- Plan lifecycle and maintenance from the outset - including patch management, end-of-support dates and an exit strategy.
❓ Frequently asked questions
What is the difference between application architecture and software architecture?
Application architecture looks at the whole landscape: which applications exist and how they work together. Software architecture describes the internal structure of a single application, such as its modules, layers and frameworks. An application architect therefore decides where a system fits in the landscape, while a software architect decides how the system itself is built.
Which tools are used for application architecture?
Application architecture is usually modelled in ArchiMate, using tools such as Archi (open source), BiZZdesign or Sparx Enterprise Architect. Many organisations also use an enterprise architecture platform or a CMDB for portfolio management. A simple spreadsheet listing applications, owners and interfaces is often a valuable first step.
Does OT software belong in the application architecture?
Yes, OT software such as SCADA, historians and MES belongs in the application architecture, even when IT does not manage it. The integrations between OT and ERP or cloud platforms are both the biggest risk and the biggest opportunity. A shared application overview makes those integrations visible and manageable.
What is an application landscape?
An application landscape is the complete overview of all applications in an organisation with their functions and interfaces, often shown as a single landscape map. It is the main deliverable of application architecture. Dutch municipalities, for example, can record their application landscape in the GEMMA Softwarecatalogus.
How does application architecture help cybersecurity?
Application architecture shows which applications support critical processes, which data they handle and through which interfaces they can be reached. That overview is needed to assess risk, define zones and quickly match vulnerabilities to affected systems. Without an application architecture, an organisation often does not know what depends on a compromised system during an incident.
📌 In summary
Application architecture describes which applications an organisation has, what they do, which data they manage and how they are connected. It links business and information architecture to the technical infrastructure, uses frameworks such as TOGAF and ArchiMate, and in the Netherlands aligns with NORA, GEMMA and WILMA. In OT environments, long lifespans, availability and zoning come on top of that.
Application architecture brings structure to the software landscape, from municipality, water board and ministry to factory, so that applications are managed strategically, securely and efficiently.