One could describe each source used in the description of each processing step, or describe all the processing steps in which each source participates in the description for the sources. A better way would be to link the source descriptions to the appropriate processing steps. The standards do this through the source abbreviations.
Assign a unique abbreviation to each source. The standards do not describe how to create the abbreviation. One means is to use the Originator and Publication Date of the source. Other styles also are possible. For example, a discipline that had a standard style for citing references in professional papers might choose that style for the abbreviation. Large organizations that have a library of source materials may choose to use the library's unique identifier for each source as the abbreviation. The most important thing is that each source must have a unique abbreviation.
Use the abbreviations to link the sources to the processing steps.
For example (see figures below), an organization (named Agency A) might compile wetlands information on an orthophoto and then digitize wetlands information. The organization wishes to document the activity using the standard and requires that the compilation and digitizing process steps be described separately. In addition, the organization obtained the orthophoto from another organization (named Company B).
Is source "Company B 1993" the source for the second processing step...?
In the first process step, wetlands are compiled onto the orthophoto (source Company B 1993). In the second step, the wetlands are digitized from the annotated orthophoto. But from what source? One choice is source Company B 1993, although that source (the orthophoto) does not have the compiled wetlands information.
Another choice is to have the first process step produce a "source" which is the annotated orthophoto. This source would be described using the Source Information element, and abbreviated as Agency A 1994. Source Agency A 1994 (the annotated orthophoto) can then be referenced by subsequent process steps.
Any data base created by merging information obtained from distinct sources shall be described in sufficient detail to identify the actual source for each element in the file. In these cases, either a lineage code on each element or a quality overlay (source data index, etc.) shall be required.
The lineage portion shall also include reference to the specific control information used. Control from the National Geodetic Reference System shall be identified according to identifiers in that system, while other points used for control shall be described with sufficient detail to allow recovery.
The lineage portion shall describe the mathematical transformations of
coordinates used in each step from the source material to the final
product. The locations of any registration points for coordinate
transformations shall be given. The methods used to make coordinate
transformations shall be documented. To fulfill this standard, it is
acceptable to make reference to separate documentation or the coordinate
transformation algorithm used, but the specific parameters applied shall
be described for the particular case. Documentation of a transformation
algorithm shall include the nature of computational steps taken to avoid
loss of digits through roundoff and shall include a set of sample
computations including numerical values of coefficients to confirm
equivalence of transformations. The documentation of a transformation
algorithm shall be available on request by a user obtaining digital data
even if that user is not licensed to use the particular software.
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