What Is API (Application Programming Interface)?
Also known as: Application Programming Interface, web service
Definition
An API (Application Programming Interface) is a defined contract that lets one software system request data or trigger functions in another, specifying the available operations, the structure of requests and responses, and the rules for authentication and error handling.
API (Application Programming Interface) Explained
An API is fundamentally an agreement about boundaries. It says: here is what you may ask me to do, here is the shape of the request, here is the shape of the answer, and here is what happens when something goes wrong. Everything behind that boundary - the database schema, the language, the deployment - can change without breaking callers, provided the contract holds. That decoupling is why APIs replaced direct database access as the sanctioned way to integrate with ERP and other systems of record.
A usable API specifies several things beyond operations. Authentication establishes who is calling, typically through OAuth 2.0 flows, API keys, or mutual TLS in higher-assurance environments. Authorization determines what that caller may see, which in ERP contexts must respect the same site, entity, and field-level restrictions a user would face. Rate limits protect the backing system from being overwhelmed. Pagination governs how large result sets are traversed. Error semantics define which failures are retryable and which are permanent.
In the ERP world, APIs sit on top of decades of existing application logic rather than replacing it. Infor SyteLine exposes its business logic through IDOs, the Intelligent Data Objects that encapsulate data access and business rules, callable through web service interfaces; Infor OS provides an API gateway that fronts those and other services with consistent security. Infor LN and Baan expose business object interfaces and generated service definitions. Salesforce and ServiceMax expose both REST and SOAP interfaces with governor limits that shape integration design.
Calling an API is not the same as integrating correctly. ERP APIs enforce business rules, and an integration that bypasses them by writing directly to tables will eventually corrupt data in ways that surface as inventory variances or unbalanced ledgers months later. Equally, an API that is called in a tight loop per record, when a bulk operation exists, will hit rate limits and lengthen batch windows. Good ERP integration design chooses the right granularity, respects transaction boundaries, and handles partial failure explicitly.
Versioning and lifecycle discipline determine long-term cost. Additive changes such as new optional fields are usually safe; removing a field, changing a data type, or tightening validation is breaking. Mature programs publish versioned endpoints, maintain deprecation timelines, and document changes in a specification such as OpenAPI so consumers can generate clients and detect drift. In regulated environments, the API contract and its change history also become audit evidence for how data moved between systems.
Why It Matters
- APIs are the sanctioned integration path into ERP, preserving business rules that direct database writes silently bypass.
- Authentication and field-level authorization on APIs determine whether integrations honor the same export control and CUI boundaries as human users.
- Rate limits and call granularity drive integration performance, deciding whether a nightly sync takes minutes or exceeds its batch window.
- Versioning discipline determines whether an ERP upgrade breaks fifteen downstream integrations or none of them.
In Practice
A defense manufacturer built a reporting integration that read ERP data through a service account with full visibility, then exposed results in a dashboard filtered in the browser. Anyone who opened developer tools could see export-controlled records the filter was hiding. Enforce authorization at the API layer using the calling user's identity, not a privileged service account plus presentation-layer filtering, whenever the data carries CUI or export controls.
Frequently Asked Questions
What is the difference between an API and a database connection?
A database connection reads and writes tables directly, bypassing application logic, validation, and security. An API invokes the application's own business logic, so posted transactions follow the same rules a user would trigger. Direct database writes to an ERP are the leading cause of silent data corruption, because constraints enforced in application code are not enforced at the table level.
How should ERP API credentials be managed?
Use dedicated integration identities rather than a person's account, store secrets in a managed vault rather than configuration files, scope permissions to only the objects and operations the integration needs, and rotate credentials on a schedule. Where the data carries CUI or export-controlled content, prefer flows that carry the end user's identity so authorization decisions reflect that user's clearance.
Related Terms
REST API
A REST API is a web interface that exposes application data as addressable resources over HTTP, using standard verbs such as GET, POST, PUT, PATCH, and DELETE, stateless requests, and conventional status codes, typically exchanging JSON.
SOAP
SOAP is an XML-based messaging protocol for exchanging structured information between systems, in which each message is an envelope containing an optional header and a body, and the available operations are formally described by a WSDL contract.
Middleware
Middleware is software that sits between applications and handles the communication, transformation, routing, and reliability concerns of moving data between them, so that the applications themselves do not need to know about each other directly.
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