Using multimodality in a computing system is advantageous in the sense that it makes computing more accessible to a wide range of users including those with impairments. Our work is aimed at making informatics accessible to the visually impaired, specially the access to mathematical expressions. The selection of modalities, media, and presentation formats depends on the interaction context (i.e. combined contexts of the user, his environment and his computing system) and nature of the expression. The adaptation of a computing system to the needs of a mobile user is essential in order that the user could continue working on his task at anytime anywhere, thereby increasing his productivity. The system design is intended to be pervasive, fault-tolerant and having a great self-adaptation capability under varying conditions (e.g. missing or defective components, change in computing resources). This paper is aimed at presenting the modeling and the simulation of our system through case studies and formal specification using Petri nets. Also we propose ontology for context modeling. A simulation of the system’s behavior, along with some test case scenarios, is also presented in this paper.