2.7 Let us sum up
Interoperability is a means to achieve global aggregation of open knowledge objects. We need internationally agreed upon standards to realize the dream of global open access infrastructure. So far there are seven levels of interoperability to handle metadata, multi-deposits, compound digital objects, usage data related to OA resources, unique resource identification, persistent author identifiers, network level exchange of OA resources and semantic level interoperability. Each of these interoperability levels are fortunately supported by various initiatives and standards. Most of these initiatives are coming with innovative solutions and standards. Many standards are considered as global de facto standards in the domain. Although all the levels are equally important, presently the metadata interoperability is the most matured area and the semantic interoperability is possibly the most futuristic in nature. It promises a new era of machine-generated meaningful exchange of OA resources across global service providers. The challenges in interoperability includes persistent identification of resources and contributors, multilingual contents transfer, managing interoperability of web aggregation, integrating OA networks operating at global scale and support for implementing interoperability standards to individual OA service providers at local level.