# Reference ```{admonition} New to OFDS? Read the [Primer](../primer/index.md). ``` ```{note} Throughout the reference documentation, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC2119](https://datatracker.ietf.org/doc/html/rfc2119). ``` The [data model reference](data_model.md) is the canonical reference for the entities, attributes and relationships that make up the Open Fibre Data Standard (OFDS) data model. The [codelists reference](codelists.md) is the canonical reference for the meaning of the codes used to limit and standardise the possible values of attributes in the OFDS data model. The [data formats reference](data_formats/index.md) is the canonical reference for the data formats in which OFDS data can be published, stored and exchanged. ```{eval-rst} .. toctree:: :maxdepth: 1 data_model codelists identifiers crs data_formats/index.md ```