This paper proposes a document oriented paradigm to the development of content-intensive, document-based applications (e.g. educational and hypermedia applications, and knowledge based systems). According to this paradigm, the main aspects of this kind of applications can be described by means of documents. Afterwards, these documents are marked up using descriptive domain-specific markup languages and applications are produced by the automatic processing of these marked documents. We have used this paradigm to improve the maintenance and portability of content-intensive educational and hypermedia applications. ADDS (Approach to Document-based Development of Software) is an approach to software development based on the document oriented paradigm. A key feature of ADDS is that formulation of domain-specific markup languages is a dynamic and eminently pragmatic activity, and markup languages evolve according to the authoring needs of the different participants in the development process (domain experts and developers). The evolutionary nature of markup languages in ADDS leads to OADDS (Operationalization in ADDS), the proposed operationalization model for the incremental development of modular markup language processors. Finally, the document-oriented paradigm can also be applied in the construction of OADDS processors that are also described using marked documents. This paper presents our ADDS approach, including the operationalization model and its implementation as an object-oriented framework. The application of our document-oriented paradigm to the construction of OADDS processors is also presented.