The paper describes the ALVIS annotation format and discusses the problems that we encountered for the indexing of large collections of documents for topic specific search engines. This paper is exemplified on the biological domain and on MedLine abstracts, as developing a specialized search engine for biologist is one of the ALVIS case studies. The ALVIS principle for linguistic annotations is based on existing works and standard propositions. We made the choice of stand-off annotations rather than inserted mark-up, and annotations are encoded as XML elements which form the linguistic subsection of the document record.