Tuesday, March 3, 2015

Metadata for Aggregated Data Sets

Aggregated or "rolled up" data is a compilation of locally sourced data assembled into a single, often standardized data set.  This often occurs at the state level such as state standardized address or parcel data.

Many consumers of aggregated data use it as produced and need no additional information about it.  Some users need additional information from local providers or need information about how source data was generated or fitness for use and need locally sourced metadata.

Metadata for a compiled or aggregated data set might describe the compilation process, any data transformation or standardization by the aggregator, and the identity of source contributors.  This could be accomplished with current metadata tools and standards, but it could be lengthy and tedious to maintain.

Another approach could be to develop metadata about each contributor and their source data set and then link those individual metadata records from the compiled metadata.  It may be difficult to associate which record in the compiled file matches which metadata file, and it may be challenging to maintain, but it could be accomplished with the current tools and standard formats.

A third approach, and one that is advocated in the PLSS Cadastral Publication standard, is to develop a spatial feature, termed metadata at a glance, that provides the geometry of the extent for each contributor, the date the source information was added to the compiled data set, the identified custodian or steward for the data, and a link to the contributors metadata about their source data.  The compiled metadata record describes how the data are aggregated and focuses on describing the compiled product, but the metadata at a glance directs users to original sources. 

Using this metadata at a glance approach, the geographic extent for each contributor can be easily viewed and the last update and perhaps an accuracy summary can be seen at a glance.  The compiled data set metadata will focus on the methods and standards of aggregation and compilation.  The currency and contributors will be readily visible and accessible through the metadata at a glance.  Links to source custodians and source data can be found from the metadata at a glance. 

Spatially enabled geospatial metadata.

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