Section 2.2.7.4.1. Introduction

(1) The Crystallographic Information File (CIF) standard is an extensible mechanism for the archival and interchange of information in crystallography and related structural sciences. Ultimately CIF seeks to establish an ontology for machine-readable crystallographic information – that is, a collection of statements providing the relations between concepts and the logical rules for reasoning about them.

Essential components in the development of such an ontology are:

(a) the basic rules of grammar and syntax, described in Sections 2.2.7.1 to 2.2.7.3;

(b) a vocabulary of the tags or data names specifying particular objects;

(c) a taxonomy, or classification scheme relating the specified objects;

(d) descriptions of the attributes and relationships of individual and related objects.

In the CIF framework, the objects of discourse are described in so-called data dictionary files that provide the vocabulary and taxonomic elements. The dictionaries also contain information about the relationships and attributes of data items, and thus encapsulate most of the semantic content that is accessible to software. In practice, different dictionaries exist to service different domains of crystallography and a CIF that conforms to a specific dictionary must be interpreted in terms of the semantic information conveyed in that dictionary.

However, some common semantic features apply across all CIF applications, and the current document outlines the foundations upon which other dictionaries may build more elaborate taxonomies or informational models.