One of the first issues undertaken by the IVOA Theory Group was the definition of query protocols adequate for theoretical data: the VO protocols already defined for observational data (Conesearch, SSAP, SIAP,...) are based on absolute positions on the sky and, in most cases, cannot be applied to theoretical models. Moreover, for theoretical models, there is not a common set of input parameters that could play the role of the coordinates for observational data as each model has its own collection of input parameters that normally differ from one model to another.
To handle this problem, SVO-LAEFF and ESA-VO proposed TSAP (Theoretical Spectra Access Protocol) as an attempt to incorporate theoretical models to the VO. With TSAP, a ``format=metadata'' dialog is used in such a way that the client can ask the server for the collection of the allowed input parameters as well as the valid values for each one of them. In this way, the client can build an adequate form for a given model and shows it to the user, who will select the preferred parameter values or ranges. Afterwards, the client will build a valid query and will send it to the data server which will give back the results in VOTable format.
A more detailed description of TSAP can be found here: lale devri
TSAP is considered part of the Simple Spectra Access Protocol (SSAP) as a use case for theoretical data.