Definition of metadata requirements for remote data access and integration in a data access layer built over MDSplus

This document proposes a possible organization for data and metadata presentation. In particular a set of rules (ontology) will be introduced for data defini tion and organization. These rules will lead to the definition of the actual data structure to be used to provide a new presentation layer above existing experiment databases, abstracting therefore from the specific storage technologies, and using MDSplus as a bridge between the actual experiment database and its view . Broadly speaking, an interface to experimental data is composed by a set of data items, organized in a hierarchical structure, where every data item can b e enriched with a set of support information (metad ata). Data types can be atomic or composite in order to d escribe more complex information. In order to provi de an unambiguous definition of the presented information it is however necessary to provide formal definiti on of the rules driving the definition of data, metadata and structures. Once such rules have been defined, the second step in the presentation layer development p rocess is the definition of the actual structure, i .e. the data and metadata items and their structure which a dhere to the given rules. The third step in the pro cess is the mapping of the defined structures onto existing and possibly remote experimental databases in orde r to present experimental data information in general wa y, providing an interface layer targeted to the dat a users, abstracting the unnecessary details in data locatio n and storage methods. A further and important step is represented by the generation of a set of tables of a relational database based on metadata. The above steps will be described in detail in the following sections, after an introduction of the ba sic concepts presented in this document.