A CIF is an ASCII file conforming to the STAR File syntax with some additional restrictions. It contains tags identifying many quantities or elements of information, and the associated values. The meanings of the tags are specified in standard library files known as CIF dictionaries, although files may also contain pieces of information defined implicitly or in non-standard dictionaries.

The specification of the CIF standard can be found on the web pages at http://www.iucr.org/iucr-top/cif.

Several standard dictionaries of data names are maintained for use in different branches of crystallography or related structural sciences. The various dictionaries and the project teams responsible for their specification and maintenance are identified by acronyms such as

coreCIF

Data names relating to the core of crystallography and to single-crystal small-molecule or ionic structural studies.

pdCIF

Data names used in powder diffraction.

msCIF

Data names used in the description of modulated aperiodic structures.

mmCIF

The dictionary used in macromolecular crystallography. It includes the data items defined in the core dictionary, but with a slightly different formalism.

imgCIF

A dictionary of terms used in the representation of images and higher-dimensional data sets.

Information on these and other specialised dictionaries may be found on the CIF home page.

Reference:
Hall, S. R., Allen, F. H. and Brown, I. D. (1991). Acta Cryst. A47, 655-685.

Nothing is necessarily "wrong" with any of these file formats listed; but typically they serve the purpose of a specific program; in some cases are undocumented or not stable over time; and are unstructured. CIF, however, is specifically designed for data exchange between software packages of many different types. It is publicly documented and intended to be very stable; and it also describes in detail the data model appropriate for the data it conveys.

But most importantly, it provides a framework for all data of crystallographic interest: raw intensity sets, reduced data sets, images, graphical representations, tables of derived data, experimental logs, or literature submissions. It has a very rich vocabulary of recognised data names drawn up by experts in crystallography. While it may be useful to transform some or all of the contents of a CIF to some or all of the above formats, the CIF remains the single most comprehensive repository of information suitable for archiving or data interchange.

STAR Files (with or without the syntax restrictions of CIF) are used in other disciplines. Examples are the NMR-STAR datasets of the BioMagResBank, the World Database of Crystallographers source files, and the Molecular Information File (MIF). Clearly, the less another STAR application departs from the restricted CIF syntax, the easier it will be to handle overlap between CIF and non-CIF applications.

Yes. A formal Backus-Naur specification of the STAR syntax was published in J. Chem. Inf. Comput. Sci. (1994), 34, p. 507.

data_chemical_melting_point
    _name                      '_chemical_melting_point'
    _category                    chemical
    _type                        numb
    _enumeration_range           0.0:
    _units                       K
    _units_detail              'kelvins'
    _definition
;              The temperature in kelvins at which a crystalline solid changes
               to a liquid.
;  

Reference:
McMahon, B. (1995). A Brief History of the DDL. http://www.iucr.org/iucr-top/cif/ddlhist.html.

DDL0 is the name sometimes given to the set of properties associated with CIF data names in the original CIF dictionary published in 1991. These have been superseded by more refined formalisms, and it is not in general considered necessary that DDL parsers should recognise these properties.

DDL version 1 is the set of properties associated with CIF data names in the coreCIF dictionary and in other CIF extension dictionaries, largely concerned with small-molecule crystallography.

References:
Hall, S. R. and Cook, A. P. F. (1995). J. Chem. Inf. Comput. Sci.. 35, 819-825.
DDL Version 1.4 Dictionary (1995). ftp://ftp.iucr.org/pub/ddldic.c95.

DDL version 2 is the set of properties associated with CIF data names in the mmCIF dictionary for macromolecular structures, and in related projects such as the imgCIF work on images. It embraces a data model that is very close to that of a relational database. CIF data names described by DDL2 include a period character `.' to indicate the category (or, equivalently, relational table) to which they have been assigned.

Reference:
DDL Version 2.1.1 Dictionary (1995). ftp://ftp.iucr.org/pub/ddl2.c96.

DDL version 3 is the name given to some work in progress by Syd Hall and his colleagues at the University of Western Australia. It is intended to build on the greater consistency and data typing abilities of DDL2 without tying the data model too closely to that of a relational database. A particular goal of DDL3 is to introduce methods into data dictionaries through a formal language known as dREL (Dictionary Regular Expression Language).

CBF is the Crystallographic Binary File. It is an outgrowth from the imgCIF project to describe area-detector and image-plate images in CIF terms. While the imgCIF dictionary allows a fully compliant CIF archive file to be created of an image, it was felt that the ASCII representation of huge data sets was unnecessarily verbose, and a packed binary representation was designed to be of more use in everyday working. The information content of a CBF is identical to that of its associated imgCIF ASCII representation: only the internal data storage (and file size) differ.