Those cases where the link is only compound-to-document can also be referred to as D-C-(or c2d). These have become available in a large excess over full DARCLP since they are technically easier to obtain and can be automated to a usable level of specificity. This needs the introduction of the intuitive concept of "aboutness" (ABNS). The title of a document from which D-C could be extracted usually includes an explicit ABNS statement. For example, the code name of a lead compound would be what a medicinal chemistry journal article would be "about". In the same way the ABNS of a clinical pharmacology journal article some years later could be describing the clinical trial results for the identical structure which, by then, could have an International Non-proprietary Name (INN). However, the extraction of multiple compounds (i.e. one-D-to-many-Cs) immediately becomes problematic in the absence of full relationship chains. For example, the med chem article may describe the testing of useful set of analogues for SAR but (as is usually the case) the A-R-P data was not extracted.