Glossary
Modernisation glossary
Plain-language definitions of the modernisation, architecture, integration and compliance terms we use, written to be quoted and to keep technical and non-technical teams talking about the same thing.
Every term we use, defined.
Grouped so you can jump to a family of ideas, or search the page for a single term. Every definition stands on its own.
Ways to modernise a system.
The strategies and techniques for changing a system that is already live, from the lowest-risk lift to a full re-architecture.
- Big-bang cutover
- A big-bang cutover is a modernisation or migration strategy in which the old system is switched off and the new one switched on in a single planned event, rather than running the two in parallel and moving across gradually. It is simpler to plan but concentrates risk: if the new system fails under real conditions there is no running fallback, which is why incremental approaches such as the strangler fig pattern are usually preferred for business-critical systems.
- Characterisation test
- A characterisation test is an automated test written to capture what an existing system actually does, rather than what it was meant to do, so that its current behaviour is pinned down before anything is changed. It is an essential tool in legacy modernisation, where undocumented rules often live only in the code: by locking in the observed behaviour first, a team can refactor or rewrite around it and detect any unintended change.
- Legacy modernisation
- Legacy modernisation is the process of updating, replacing or re-engineering ageing software systems so they meet current performance, security, integration and maintainability needs. It can range from moving a system to modern infrastructure to fully re-architecting it, and is usually done incrementally to limit risk to the business.
- Rearchitect
- To rearchitect an application is to significantly change its fundamental structure, for example by breaking a monolith into services or adopting an event-driven or composable design. It is the most far-reaching modernisation option short of a full rewrite, undertaken when the existing architecture can no longer meet the organisation's needs.
- Refactor
- Refactoring is improving the internal structure of existing code without changing its external behaviour, making it cleaner, easier to understand and easier to extend. In modernisation, refactoring reduces technical debt and prepares a system for further change while keeping it working as before.
- Rehost (lift-and-shift)
- Rehosting, often called lift-and-shift, is moving an application to new infrastructure, such as the cloud, with little or no change to its code or design. It is usually the fastest and lowest-risk modernisation option, though it does not by itself address underlying technical debt or architectural limitations.
- Replatform
- Replatforming is moving an application to a new runtime, database or platform while making targeted changes to take advantage of it, without fully rewriting the application. It sits between rehosting and rearchitecting, offering some modernisation benefits, such as managed services or better scalability, with moderate effort and risk.
- Strangler fig pattern
- The strangler fig pattern is a technique for modernising a legacy system gradually by building new functionality around it and incrementally redirecting traffic to the new components until the old system can be retired. It lets a replacement grow alongside the original in production, avoiding the risk of a single big-bang cutover.
The architecture and integration ideas.
How modern systems are structured and connected, and the vocabulary we use to describe them.
- API
- An API (application programming interface) is a defined set of rules that lets one piece of software request data or actions from another in a predictable way. APIs are the contracts that allow separate systems, services and applications to work together without needing to know each other's internal details.
- Composable architecture
- Composable architecture is an approach to building systems from independent, interchangeable components connected through well-defined APIs, so each capability can be developed, replaced or scaled on its own. It increases flexibility and reduces vendor lock-in because parts of the system can change without rebuilding the whole.
- Enterprise application integration (EAI)
- Enterprise application integration (EAI) is the practice of connecting an organisation's separate business applications so they can share data and processes as a coordinated whole. It typically uses middleware, messaging and APIs to avoid isolated data silos and manual re-keying between systems.
- Event-driven architecture
- Event-driven architecture is a design style in which components communicate by producing and reacting to events, such as 'order placed' or 'payment received', rather than calling each other directly. This loose coupling makes systems easier to scale and extend, because new components can respond to existing events without changing the producers.
- MACH architecture
- MACH architecture is a set of principles for building flexible, cloud-based systems, standing for Microservices, API-first, Cloud-native and Headless. Systems built this way are composed of independent services that communicate through APIs, run natively in the cloud and separate the front-end experience from back-end logic, making them easier to evolve and replace piece by piece.
- Observability
- Observability is the ability to understand the internal state of a software system from the data it produces, primarily logs, metrics and traces. Good observability lets teams detect, diagnose and resolve problems quickly, and is essential for running modern distributed and event-driven systems reliably.
- Systems integration
- Systems integration is the work of connecting separate applications, services and data sources so they operate together as a coherent whole. It typically involves APIs, messaging and data mapping to ensure information flows correctly between systems and to remove manual, error-prone handoffs.
The systems you already run.
The platforms and workarounds that make up a typical legacy estate, and why they are hard to replace.
- BSS/OSS
- BSS/OSS refers to the two families of systems that telecommunications operators run: Business Support Systems (BSS), which handle customer-facing concerns such as billing, ordering and customer management, and Operational Support Systems (OSS), which handle network operations such as provisioning, inventory and fault management. They are frequently the focus of modernisation and integration work because they are large, interconnected and often built on legacy technology.
- ERP
- ERP (enterprise resource planning) is a category of integrated software that organisations use to manage core business processes such as finance, procurement, inventory, manufacturing and human resources in a single system. Because ERP platforms sit at the centre of operations and are costly to change, they are common subjects of modernisation, integration and lock-in concerns.
- Legacy system
- A legacy system is older software that remains in active use because it still supports important business functions, even though its technology, design or tooling is outdated. Such systems are often hard to change, costly to maintain and difficult to integrate with newer software, which is what makes them candidates for modernisation.
- Shadow system
- A shadow system is an unofficial tool (often a spreadsheet, script or small database) that people build and rely on outside the sanctioned systems to get their work done. Shadow systems matter in modernisation because they hold real business logic and dependencies that no official documentation records, and missing them during discovery is a common reason a legacy system cannot be switched off on schedule.
What legacy quietly costs.
The risks and running costs that accumulate in ageing systems, and the words for naming them.
- Bus factor
- The bus factor is the number of people who would have to be lost before critical knowledge about a system disappears with them, the grim shorthand being how many could be 'hit by a bus'. A bus factor of one, where a single person understands how something works, is a common and serious risk in legacy systems, and reducing it through documentation, clearer code and shared ownership is a frequent goal of modernisation.
- Dual-running cost
- Dual-running cost is the ongoing expense of operating an old system and its replacement at the same time during a modernisation: typically licences, infrastructure, patching and the effort of keeping two sets of data consistent. Because a legacy system often stays live long after a new one launches, dual-running cost is easy to underestimate and, once quantified, frequently makes the business case for finishing the job and decommissioning the old system.
- Technical debt
- Technical debt is the future cost created when software is built or changed in a way that is quick now but harder to maintain later, much like financial debt that accrues interest. Left unmanaged it slows delivery, increases defects and raises the risk of change, which is why addressing it is a core part of modernisation.
- Vendor lock-in
- Vendor lock-in is the situation where moving away from a particular supplier, platform or technology becomes prohibitively costly or difficult, limiting an organisation's freedom to change. It is mitigated through open standards, clear API boundaries, portable data and composable designs that keep components replaceable.
Data protection and regulation.
The rules that shape how systems in the UAE and beyond must handle personal data.
- GDPR
- The GDPR (General Data Protection Regulation) is the European Union's data-protection law governing how organisations collect, process and store the personal data of individuals in the EU. It sets requirements around lawful basis, consent, data subject rights and security, with significant penalties for non-compliance, and it applies to many organisations outside the EU that handle EU residents' data.
- UAE PDPL
- The UAE PDPL (Personal Data Protection Law) is the United Arab Emirates' federal framework governing how personal data is collected, processed and protected. It establishes obligations for organisations handling personal data and rights for individuals, and shapes how systems operating in the UAE must manage data privacy and security.
See these ideas applied to real systems?