Standardization is required at different levels, first, when resources are created, technologies, policies and formats compatible with what is common in the sector must be considered; second, when these resources are included in a repository, and must be described, schemas will be used to ensure their easy location and compatibility with other metadata systems; third, when those resources are used and have to be incorporated into different services, repositories, platforms and applications in a given context; and fourth, when the systems involved in an environment have to interoperate with others to fulfill their functions or expand their capabilities.