Active business process support utilizing workflow technology is promising for building information systems that are flexible regarding both business and corresponding IT infrastructure transformation. To achieve this, conceptual models of work processes have to be aligned with interests of several stakeholders, including business professionals and users. In particular, user access to process models presuppose comprehensible in addition to expressive models. We propose a framework for evaluating quality in process modeling languages (PMLs) and models. It is applied to a representative sample of flexible workflow products and prototypes. We study the properties of the various products? underlying PMLs, and derive their first cut ontology, or meta-model. In carrying out the evaluation, we show the applicability of our framework, and point out some research opportunities in areas where the products differ widely or carry similar deficiencies.