What Is an IDL (Interface Definition Language)?

March 27, 2024

An Interface Definition Language (IDL) defines the interface that programs or systems should use when communicating with each other. IDLs are used to describe the types, methods, and data formats that two or more software components must use to interact, typically across different programming languages or networked environments. The goal of an IDL is to ensure interoperability by providing a clear, language-agnostic interface specification.

IDLs are particularly useful in distributed systems, where components run on different platforms or are written in different programming languages. By defining interfaces in an IDL, developers can generate code that allows these diverse components to communicate. This seamless communication is crucial in many domains, such as web services (using WSDL for SOAP or GraphQL for APIs), object request brokers (like CORBA), and remote procedure calls (RPC), including modern implementations like gRPC.

A Brief History of IDL (Interface Definition Language)

The concept of Interface Definition Languages (IDLs) has evolved alongside the development of distributed computing and the need for diverse systems to communicate. The history of IDLs is intertwined with the evolution of computer networking, remote procedure calls (RPC), and object-oriented programming.

The roots of IDL can be traced back to the development of remote procedure call (RPC) mechanisms in the 1970s. RPC allowed functions to execute on a remote system as if they were local, necessitating a way to define the interfaces for these remote functions.

In the 1980s, technologies like Sun's RPC began formalizing the use of IDLs to define the interfaces for remote procedure calls. Sun RPC used an IDL to specify the data types and signatures for remote functions, enabling different systems to communicate over a network.

The Object Management Group (OMG) introduced the Common Object Request Broker Architecture (CORBA) in the late 1980s. CORBA's IDL allowed for the definition of interfaces for objects that could be invoked remotely, playing a crucial role in the adoption of object-oriented approaches in distributed computing.

The 1990s saw the expansion of IDLs into various domains. Microsoft introduced the Component Object Model (COM) and the Distributed Component Object Model (DCOM), which used IDL to define interfaces between components in a networked environment.

The internet's growth led to the development of web services and the use of Web Services Description Language (WSDL) as an IDL for defining web service interfaces. WSDL allowed different web services to communicate using XML-based messages, regardless of the underlying programming languages or platforms.

The 2000s and onwards have seen the introduction of newer IDLs and serialization formats designed for more efficient communication and better support for modern programming paradigms. Examples include Google's Protocol Buffers (Protobuf), which is used with gRPC for high-performance RPC, and Facebook’s Apache Thrift, which is used for scalable cross-language services development.

The advent of APIs and microservices architecture has emphasized the importance of IDLs for defining clear, robust interfaces between services. GraphQL, developed by Facebook in 2012 and open-sourced in 2015, provides a powerful IDL for defining data queries and manipulations in a flexible, efficient manner.

Today, IDLs continue to evolve, with ongoing development focused on improving performance, interoperability, and the ability to handle complex data structures and workflows. The trend toward cloud computing, microservices, and containerization further underscores the importance of efficient, well-defined interfaces for communication between distributed systems.

Interface Definition Language Use Cases

Interface Definition Languages (IDLs) serve a variety of purposes in software development and system integration, addressing the need for clear and consistent definitions of how different software components interact. Here are some key use cases for IDLs:

  • Remote Procedure Call (RPC) systems. IDLs define the interfaces for functions or procedures that can be executed on a remote system, facilitating communication between services running on different computers or networks. This is crucial for distributed systems where parts of an application are spread across different locations.
  • Object Request Brokers (ORBs). In systems like CORBA (Common Object Request Broker Architecture), IDLs describe the methods and data types of objects that can be called remotely. This allows objects in different programming languages or on different platforms to communicate with each other seamlessly.
  • Web services. For SOAP-based web services, WSDL (Web Services Description Language) acts as an IDL, defining the operations available over the web service and the format of request and response messages. This ensures interoperability between web services and their clients, regardless of their underlying implementations.
  • API development. IDLs are used to define the endpoints, request/response structures, and behaviors of APIs. This is particularly relevant in RESTful APIs and more modern GraphQL APIs, where the IDL specifies the schema for queries, mutations, and the data types exchanged between the client and server.
  • Microservices architectures. In microservices architectures, IDLs facilitate the definition of clear contracts between different services. This allows for independent development and deployment of services while ensuring they can communicate effectively, which is essential for the agility and scalability of microservices-based applications.
  • Cross-language development. IDLs enable the generation of code stubs in multiple programming languages, allowing for the integration of components written in different languages. This capability is beneficial in complex systems where different components may be optimized by implementing them in languages best suited for their tasks.
  • Data serialization and deserialization. Technologies like Google's Protocol Buffers use IDLs to define structured data. This enables efficient serialization and deserialization of data for storage or transmission, optimizing communication between different parts of a system or across network boundaries.
  • System documentation. IDLs provide formal, machine-readable documentation of a system's interface, which can be used to generate human-readable documentation or guide the development of client libraries and tools. This capability enhances understanding and facilitates the integration of different software components.

Software Based on IDL – Examples

Here are the most common examples of software that utilizes IDL capabilities:

  • CORBA (Common Object Request Broker Architecture). CORBA uses its own IDL to define the interfaces that objects present to the outside world, enabling seamless communication between objects no matter where they are located or what language they are written in. CORBA IDL is crucial for defining cross-language and cross-platform object interfaces.
  • gRPC (Google Remote Procedure Call). gRPC uses Protocol Buffers (Protobuf) as its IDL, which allows developers to define simple services and their method parameters and return types. It's an open-source RPC framework that enables client and server applications to communicate transparently and makes it easier to build connected systems. gRPC is designed for both high-performance and high-productivity design of distributed applications.
  • Web Services (SOAP and WSDL). For SOAP-based web services, WSDL (Web Services Description Language) serves as the IDL, describing the network service interfaces in a machine-processable format. WSDL defines how to access a web service, including the operations the service exposes, the messages used, and the protocol bindings. This standardization enables different systems to interact over the web through defined interfaces.
  • Thrift (Apache Thrift). Apache Thrift uses its IDL to define and create services for numerous languages. It provides the tools to write services that seamlessly work between C++, Java, Python, PHP, Ruby, Erlang, Perl, Haskell, C#, Cocoa, JavaScript, Node.js, Smalltalk, OCaml, and Delphi and other languages. Thrift is designed to be efficient and to make writing cross-language services easier.
  • GraphQL. GraphQL uses a schema definition language (SDL) to define the structure of data that can be queried from a server. It specifies the types of data, the relationships between types, and the queries and mutations available. Unlike traditional IDLs, which define interfaces for procedure calls, GraphQL focuses on data access and manipulation. It allows clients to request exactly the data they need, making it highly efficient for complex applications and microservices.
  • Protocol Buffers (Protobuf). Protocol Buffers, developed by Google, use a simple IDL to define structured data. This schema then compiles into source code in various languages, allowing for easy serialization and deserialization of structured data. Protobuf is widely used in RPC systems, data storage, and communication protocols to ensure compatibility across different systems and languages.

Anastazija is an experienced content writer with knowledge and passion for cloud computing, information technology, and online security. At phoenixNAP, she focuses on answering burning questions about ensuring data robustness and security for all participants in the digital landscape.