An instructional application consists of a set of resources and activities to implement interacting, interrelated, and structured experiences oriented towards achieving specific educational objectives. The development of computer-based instructional applications has to follow a well defined process, so models for computer-based instructional applications have been proposed. Some of these models are oriented towards implementing products delivered in a rather specific technical platform. But specifying instructional applications using generic formats that are independent from the implementation platform, as Educational Modelling Languages do, makes it possible to improve their interoperability as well as their reusability. The work presented here proposes a specification framework based on two formalization levels. A first level proposes a meta-model to specify an instructional application by means of two models to represent the application from two different perspectives: the semantic model gathering its structure and the instructional relationships existing among its components; and the operational model to establish the application operation and behaviour. The second level of the framework implements the application model, which uses XML technologies to represent and process its components, relationships, and behaviour. A tool has been developed to visualize the specification of the model entities as well as to check some properties of the instructional application. (Contains 12 figures.)