Section 5.4.7. Name aliases

CIF dictionaries written in DDL2 permit data names to be aliased or equivalenced to other data names. This serves two purposes. First, it allows for the different data-name structures used in DDL1 and DDL2 dictionaries, and, second, it links equivalent data names within the DDL2 dictionary. Aliasing also allows the use of synonyms appropriate to the application.

CIFtbx is capable of handling aliased data names transparently so that both the input CIF and the application software can use any of the equivalent aliased names. In addition, an output CIF may be written with the data names specified in the CIFtbx functions or with names that have been automatically converted to preferred dictionary names. If more than one dictionary is loaded, the first aliases have priority. We call the preferred dictionary name the `root alias'.

The default behaviour of CIFtbx is to accept all combinations of aliases and to produce output CIFs with the exact names specified in the user calls. The interpretation of aliased data names is modified by setting the logical variables alias_ and aliaso_. When alias_ is set to .false., the automatic recognition and translation of aliases stops. When aliaso_ is set to .true., the automatic conversion of user-supplied names to dictionary-preferred alias names in writing data to output CIFs is enabled. The preferred alias name is stored in the variable dicname_ following any invocation of a getting function, such as numb_ or test_. If alias_ is set to .false., dicname_ will correspond to the called name. The variable tagname_ is always set to the actual name used in an input CIF.

For example, the data name _atom_site_anisotrop.u[1][1] in the DDL2 mmCIF dictionary is aliased to the data name _atom_site_aniso_U_11 in the DDL1 core CIF dictionary. In the example application of Fig. 5.4.7.1, showing the CIFtbx function test_ run with both the mmCIF and core dictionaries loaded, the specified data name _atom_site_aniso_U_11 is used to inquire as to the names used in an input CIF.

Figure 5.4.7.1 | top | pdf | Example application accessing aliased data names.

The execution of this code results in the following printout.