The International Virtual Observatory Alliance (IVOA) works towards standardising interoperability and curation of data and service holdings of the global astrophysical community. Within the IVOA, the Data Access Layer (DAL) Working Group's goal is to provide Recommendations (an IVOA term for the released technical standards) for accessing data collections and catalogues; filtering data holdings based on their metadata; and retrieving the ones in scope, or operating on them.
In recent years the DAL community has addressed the multi-dimensional and multi-wavelength scenarios, and kept core standards up-to-date. It has also tackled new topics such as the observation location and object visibility information retrieval, and looked at older topics such as the outstanding cases of time domain and radio astronomy data.
DAL work in the next few years will involve a mixture of revising existing standards, listening to feedback on recently updated and released standards and the specification of new standards. The DataLink 1.1, DALI 1.2, ADQL 2.1 and ConeSearch 1.1 standards are being revised. The work on these will provide new features requested by the community, updates to match the current technical landscape, and integration of changes from other Recommendations. Other specifications have been recently updated (e.g. TAP 1.1) or are waiting further community feedback before starting a revision process (e.g. SIAP 2.0 and SODA 1.0). New protocols are under development such as the Object Visibility Simple Access Protocol (ObjVisSAP) and the Provenance TAP (ProvTAP) interface. ProvTAP is being managed together with the Data Model Working Group (DM), as is the Observation Locator TAP interface, since they include data model efforts.
Community feedback and contributions are needed for all DAL activities. Particularly important are the experiences of data providers and projects that are using VO technologies to address their scientific community's requirements. This is not a trivial task since the development of a standardised interface for the final user often requires more than one Recommendation to be implemented.
This submission aims to summarise the current DAL status and progress, in order to help new end-users understand how DAL can be beneficial. It also discusses the future changes to DAL standards. Finally, it lists topics (No-SQL, code-to-data, parametric querying, actionable retrieval, ...) worth investigating in the future to keep access layer standardisation up to date with current needs.