Keywords

A data record contains zero or more (typically many) named keywords that each map to a value of a simple type such as integer, float or string associated with the record. Keywords are often used to store meta-data describing properties, history and/or context of the main image/observable data stored in the record's data segments. This is a concept familiar from standard file-based data formats, such as FITS, where the FITS header keywords would correspond to the JSOC keywords and the primary binary arrays or tables would correspond to the JSOC data segments.

In the JSOC catalog keywords values will be stored in database tables separate from the files holding the data segments. This makes it possible to

• modify keyword values without having to locate, access and possibly rewrite files on disk or tape,
• rapidly finding data records whose keywords satisfy a given condition by executing a database query,
• rapidly extract time series of the values of keywords from all or a subset of records in a series. This can be useful for, e.g., trend analysis or time series analysis of global properties, e.g. mean value or other image statistics, of data products.

There will be one database table for each series containing the values of keywords and links for all data record in the series. The values for a single data record will be contained in a single row in that table.