Services are an increasingly important part of the Web, and they are a necessary component of the semantic Web. Semantic Web services (SWS) are a research effort towards automation of the use of Web services, enhancing existing SOA capabilities with intelligent and automated integration. We have introduced WSMO-Lite, a lightweight service ontology intended for semantic annotations of the Web Service Description Language WSDL. In contrast to preceding SWS frameworks such as OWL-S and WSMO, WSMO-Lite simplifies the semantic descriptions and enables bottom-up semantic annotation of Web services, but very importantly, it also relaxes the requirements on completeness of semantic descriptions, which enables building incremental layers of semantics on top of existing service descriptions. In this work, we describe various useful subsets of the extent of semantic annotation on Web services with respect to the requirements of SWS automation tasks; and we detail the means of validating SWS descriptions with flexible levels of strictness.