This is an evolving reference document which provides a detailed
specification of a Dictionary Description Language (DDL) designed to
support macromolecular structure applications.
The DDL described here represents the largely relational DDL
presented at the CIF
Workshop in Brussels by John Westbrook, which was subsequently modified by
Syd Hall and John Westbrook to be more conforming with existing
applications of STAR
[3,2,6,5] and
CIF [4].
The DDL presented here extends the DDL that is currently
used by STAR and CIF applications in several important ways. Although
these extensions have been introduced primarily to address
problems that have surfaced in developing a macromolecular CIF
dictionary, they are sufficiently general to be useful
in a wide variety of applications.
Extensions to the current DDL have been introduced in a manner that provides the greatest degree of backward compatibility with existing CIF and STAR applications. Although the extensions introduced in this DDL have a rather profound effect on the structure of the DDL, dictionaries based on the new DDL can have the same simple appearance as dictionaries based on the current DDL. And even though a different convention is used to name data items in this DDL, an alias feature has been added to ensure that any published data item names will remain valid. In fact, the alias name mechanism provides for complete backward compatibility for all existing data files. It is hoped that the transition from the DDL in current use to this new DDL should not be difficult.