dREL is a machine-actionable language describing data relationships and designed to be embedded in DDLm dictionaries. The language is defined both explicitly in the dREL publication [1] and implicitly by the dREL code appearing in the DDLm core CIF dictionary. Note that the code in the core CIF dictionary significantly expands the language presented in the paper, for example, by adding category methods.
The present changes are relatively trivial and intended to simplify and clarify the syntax. Following proposals will be more substantial.
The proposal: A leading underscore in front of a variable is optional, and has no significance. Its use is deprecated.
The dREL paper states that the value of a data name from a Set
category can be accessed by using the form <category>.<name> in a
dREL script, for example cell.volume (p 1919, "Data References in
dREL"). However, the dREL methods in the current core CIF dictionary
and the dREL paper almost always use a form with a leading underscore,
i.e. _<category>.<name>.
The paper does not explain the appearance of the underscore in the
example methods presented there. It is possible that the underscore is
provided as a way to disambiguate ordinary variables from dictionary
items; however, as a period character must appear in a dictionary
reference, and may not appear in a variable, such disambiguation is
unnecessary. It is also important to note that the period character
is an operator in dREL, so the construction cell.volume is formally
referring to the volume column in the current packet of the cell
category. In this context, the leading underscore is potentially
misleading.
The with statement is available to alias category names in any
situation where a category name may collide with a language keyword.
The proposal: newline should be treated as ordinary whitespace.
If newline is treated as ordinary whitespace it is not significant for separating expressions. However, the dREL paper Appendix, Section 4, states that "dREL supports the following expression terminators: ... newline closes a line unless a balancing [bracket] is missing", which may be construed as allowing newline to terminate an expression.
The draft dREL grammar at the COMCIFS/dREL repository assumes that newline is whitespace. The example parser automatically generated from this grammar does not identify any problems with the grammar. Nick Spadaccini has advised that newline was not meant to be significant in the dREL grammar.
[1] Spadaccini et. al, (2012) J. Chem. Inf. Model. **52**(8) pp 1917-1925