Web Service Interfaces: A Comparative Analysis of SOAP vs. REST
Summary
A comparative analysis of two major trends in web service interfaces, SOAP and REST, a key topic for the Information Processing Engineer exam. Learn the differences between the classic SOAP, WSDL, UDDI trio and the modern REST architecture, and test your knowledge with exam-style questions.
💡 Understanding the history of web service interface methods and the role of each technology is a key point for the Information Processing Engineer exam. This post compares the classic representative, SOAP, with the modern REST to clarify their differences.
🏛️ Web Service Interfaces: Two Approaches
A web service is a way for different systems to interact over the internet. There are two main approaches to the interfaces for this interaction. One is the classic stack (SOAP, WSDL, UDDI), which explicitly defines everything, and the other is the modern style (REST), which follows the principles of the web.
Let's use the analogy of booking and ordering at a restaurant.
1. The Classic Web Service Trio: SOAP, WSDL, and UDDI
In the early 2000s, enterprises used these three technologies as a set for stable and standardized system integration. Their goal was to "find out where a service is (UDDI), check its user manual (WSDL), and then communicate according to the defined rules (SOAP)."
UDDI (Universal Description, Discovery, and Integration)
- Role: A 'phone book' or 'restaurant guide' for web services.
- Description: It acts as a search engine to find out which restaurant (service) is where and what kind of food it serves. It is rarely used today.
WSDL (Web Services Description Language)
- Role: A 'detailed menu' or 'user manual' for a service.
- Description: This is the detailed menu of the restaurant found through UDDI. It describes in great detail, in XML format, what dishes (methods) are available, the price of each dish (parameters), and what information (data types) needs to be provided when ordering.
SOAP (Simple Object Access Protocol)
- Role: A 'formal order form' following a set format.
- Description: After reviewing the WSDL menu, you place an order (request) in a very formal manner according to a set format. It uses a very strict XML message, like saying, "This order is written according to the SOAP specification..."
Summary: The classic approach is like visiting a new city, finding a restaurant with a guidebook (UDDI), reading a thick menu (WSDL) thoroughly, and then submitting a formal order form (SOAP). The process is complex but very clear and reliable.
2. The Star of Modern Web APIs: REST
In reaction to the complexity of the SOAP approach, the simpler and more web-friendly REST (Representational State Transfer) style emerged and has become the mainstream for web APIs today.
- Role: A 'design philosophy' that makes the most of the web's basic principles (HTTP).
- Description:
- No separate guidebook (UDDI) is needed. It is assumed that you already know the restaurant's address (URI). (e.g.,
https://example.com/dishes/pasta) - No thick menu (WSDL) is needed either. You communicate with simple, universally understood actions (HTTP methods), such as saying, "Show me the menu (
GET)" or "I'll order this (POST)." - Instead of a complex order form (SOAP), you make a request by writing it down on a simple memo (usually JSON).
- No separate guidebook (UDDI) is needed. It is assumed that you already know the restaurant's address (URI). (e.g.,
Summary: The REST approach is like going to a regular restaurant and ordering comfortably with just a few words. It is much faster, more flexible, and easier to learn.
📊 SOAP-based Approach vs. REST Style Comparison
| Category | SOAP, WSDL, UDDI Stack | REST Style |
|---|---|---|
| Concept | Protocol: Strict rules | Architectural Style: Flexible principles |
| Data Format | XML only | JSON, XML, etc., used freely (mostly JSON) |
| Communication | Can use other protocols besides HTTP | Works only over HTTP (maximizes HTTP features) |
| Complexity | High (requires WSDL, schema, etc.) | Low (only need to know HTTP and URI) |
| Performance | Relatively slow and heavy | Fast and lightweight |
| Primary Use | Enterprise systems requiring high security/transactions | Most public APIs, mobile apps, web services |
📝 Exam Preparation Problems
| Problem | What is the language that describes the specifications of a web service, such as the functions it provides, its parameters, and data types, in XML format? |
| Your Answer | |
| Correct Answer | Reveal Answer |
| Problem | What is the protocol with very strict rules that exchanges XML-based messages over protocols like HTTP and SMTP to invoke remote procedures? |
| Your Answer | |
| Correct Answer | Reveal Answer |
| Problem | What is the software architectural style based on the principles of identifying resources through URIs and expressing actions on those resources through HTTP methods? |
| Your Answer | |
| Correct Answer | Reveal Answer |
| Problem | What was the technology, acting as a 'phone book' for web services, that was formerly used to discover and register web services? |
| Your Answer | |
| Correct Answer | Reveal Answer |
| Problem | Compared to SOAP, what is the primary data format that is a key advantage of REST, enabling lighter and faster data exchange? |
| Your Answer | |
| Correct Answer | Reveal Answer |