Unsupported Z39.50 Access Points result to query failures and/or inconsistent answers, in spite of the protocol specification for a unified global access mechanism. A challenge to this issue is to substitute an unsupported Access Point with others, so that the most similar semantics to the original Access Point can be obtained. In this paper, we describe the Bib-1 Access Points Semantics of the Z39.50 protocol using the RDF Schema language, based on the official semantics specification of the Z39.50 Bib-1 Attribute Set. Moreover, we suggest two algorithms for the substitution of unsupported Access Point exploiting semantics information from the RDFS graph. The algorithms produce the set of Access Points, the proper combination of which produces semantics similar to the original Access Point. Then, we optimize the resulting set of Access Points by producing the minimal set of them with the closest semantics to the original one. Finally, we present an implementation where Z39.50 searches could be done using our Access Point substitution algorithms.