Application programming interface ("API")

An application programming interface, or API, is the set of rules, formats, functions and calling conventions through which a program offers its services to another program. It is distinct from the code that implements those services. Its protection falls under copyright in software, governed by Articles L. 112-2 and L. 122-6 et seq. of the French Intellectual Property Code, which implement Directive 2009/24/EC and confine protection to the expression of the program, excluding the ideas and principles underlying its interfaces.

Limited protection under copyright

The Directive states that the ideas and principles underlying any element of a program, including its interfaces, are not protected by copyright. The Court of Justice of the European Union infers from this that neither the functionality of a program, nor the programming language, nor the format of the data files used to exploit certain functions constitutes a protected form of expression. The specification of an interface, regarded as a set of functional rules, therefore falls in principle outside the monopoly. By contrast, the code that implements the interface, the written documentation and, to some extent, the original structure or organisation of the elements may benefit from software protection or from the general law of copyright, subject to originality.

Interoperability and decompilation

Union law makes interoperability an explicit objective. The lawful user of a program may observe its functioning in order to determine its ideas and principles, and may carry out decompilation to the extent strictly necessary to obtain the information needed to achieve the interoperability of an independently created program, where that information is not readily available. That right cannot be excluded by contract. It does not allow the code to be reproduced beyond what is necessary, nor the creation of a substantially similar program.

Contractual framework and other forms of protection

In the absence of a monopoly over the specification, control of access to an interface rests mainly on contract. The terms of use of an open interface set out the permitted uses, call volumes, attribution, ownership of the data exchanged and termination clauses, which operate alongside the software licence or the service agreement. An interface may also form part of a computer-implemented invention where it contributes to a technical effect, and access keys or unpublished protocols may be protected as trade secrets.

Key points

The specification of an application programming interface is not protected by copyright: only its original implementation and documentation are. Interoperability justifies observing and, under strict conditions, decompiling a program in order to connect to it. Control of an interface therefore depends on a precise contractual framework and, where appropriate, on secrecy or patents. Before reproducing a third-party interface, check that only the specification is taken over and that the code is not copied.

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This glossary entry is general in scope and does not constitute legal advice.

Dhenne Avocats is a patent litigation firm. Matters outside that field, such as trade marks, designs, copyright and IT contracts, are handled by practitioners the firm works with regularly, and by the firm itself when they arise in a patent dispute.

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