REST (Representational State Transfer) and SOAP (Simple Object Access Protocol) are two standards for building web service interfaces that allow applications to communicate over HTTP. SOAP is the older standard — it uses XML-formatted messages wrapped in a SOAP envelope, requires a formal service contract defined in a WSDL (Web Services Description Language) document, and enforces strict message schema validation. SOAP was the dominant web service standard in enterprise middleware through the 2000s and remains in use in many legacy enterprise applications (Oracle EBS uses SOAP-based web services for many of its process integrations). REST is the modern standard — it uses HTTP methods (GET, POST, PUT, DELETE, PATCH) directly on resource URLs, typically with JSON payloads, without requiring a formal contract document. REST is simpler to implement, easier to test (any HTTP client can call a REST API), and faster to work with than SOAP — which is why REST has become the dominant standard for cloud applications, including all Oracle Cloud (EPM Cloud, Fusion, OIC) REST APIs and the ZATCA Fatoora API.
REST vs SOAP Comparison
| Characteristic | REST | SOAP |
|---|---|---|
| Protocol | HTTP(S) — any HTTP method | HTTP(S) or other transport — always uses POST |
| Message format | JSON (most common), XML, or plain text | Always XML within a SOAP envelope |
| Service contract | OpenAPI/Swagger specification (optional but recommended) | WSDL (mandatory — defines all operations and message schemas) |
| Error handling | HTTP status codes (200, 400, 404, 500) + optional error body | SOAP Fault element within the XML response |
| Statefulness | Stateless — each request is independent | Can be stateful — supports WS-* standards for transactions, security, reliability |
| Oracle EPM Cloud | REST API — all Oracle EPM Cloud management and data operations | Legacy SOAP services in older Oracle EBS integrations |
| ZATCA Fatoora API | REST — JSON payloads for invoice submission and status | Not used |
| Oracle EBS | REST (Oracle EBS REST API in version 12.2+) | SOAP (legacy EBS web services, still widely deployed) |
Practical Implications for GCC Oracle Integrations
In GCC enterprise Oracle environments, both REST and SOAP are encountered in the same integration landscape. Oracle EPM Cloud (EPBCS, FCCS, ARCS) uses REST APIs exclusively — the EPM Cloud REST API provides endpoints for all job management, data operations, and metadata operations; EPM Automate CLI wraps these REST calls for command-line automation. Oracle EBS 12.2+ provides both REST APIs (for newer business objects) and SOAP web services (for legacy objects where REST equivalents have not yet been built). Older EBS integrations built against SOAP services must be maintained as SOAP-based until the EBS object has a REST equivalent — which Oracle adds incrementally across EBS versions. When migrating from Oracle EBS to Oracle Fusion, the SOAP-to-REST transition is one of the integration modernisation benefits: Fusion’s APIs are REST-first, eliminating the WSDL parsing and XML envelope construction overhead that SOAP-based EBS integrations require.
What Goes Wrong in Practice
The most common REST API integration failure in production finance automation is inadequate OAuth token lifecycle management — the automation obtains an OAuth access token at the start of the integration flow, but the token expires (typically after 60 minutes) before the integration completes its full processing cycle, producing authentication errors mid-flow. Every REST API integration must implement token refresh logic — detecting token expiry before each API call and obtaining a new token if the current one is within N minutes of expiry — rather than assuming a single token obtained at flow initiation remains valid throughout the flow’s execution.
How Loop Wise Solutions Implements REST and SOAP Integrations
We implement REST API integrations for all Oracle EPM Cloud and ZATCA Fatoora connectivity — using Oracle Integration Cloud’s pre-built REST adapters — and maintain SOAP-based integrations for Oracle EBS legacy web services where REST equivalents are not yet available. All API integrations are built with token lifecycle management, retry logic for transient errors (429 rate limit, 503 service unavailable), and response validation that confirms the API’s returned data meets the expected schema before downstream processing begins.
