What is Metadata?

Documents may contain information about the document itself: we call this metadata. For instance, a raster image file contains metadata recording the image's width and height; a word processing document may contain metadata recording the document's author and title. Metadata can be represented by key-value pairs. For instance, a document's title can be represented as the key "Title" and the value "Annual Report". We refer to a single metadata key-value pair as a metadata field.

Containers (documents with subfiles) can contain metadata about their subfiles. For instance, a Personal Folders (.pst) file is a container that can have multiple email messages as subfiles. A PST file may contain metadata, including the "To" and "From" fields of these subfiles.

Access Metadata using the C API

You can access subfile metadata using the Extract interface function fpGetSubFileMetadataList().

KeyView uses the structures KVMetadataList and KVMetadataElement to store metadata.

  • The KVMetadataList structure represents a list of KVMetadataElement objects, allowing you to iterate over them. The order of elements within the list is not significant and may change in the future.
  • The KVMetadataElement structure represents one metadata field. It contains a string representation of the field’s key, and the field’s value stored in an appropriate type.

Mail Metadata

The metadata for an e-mail message (the header fields such as "To", "CC", "Subject", and so on) are typically stored in the mail container (such as an MSG or EML file). To access this metadata you can call the function fpGetSubFileMetadataList(), in the Extract API.

The message body and any attachments are considered by KeyView as subfiles of the container. When you extract the message body, KeyView includes the header fields (by default). If you do not want to include this information, set the flag KVExtractionFlag_ExcludeMailHeader when you call fpExtractSubFile(). You might want to do this if you have already accessed the metadata and do not want to process it again.

Backwards Compatibility

To help you migrate from fpGetSubFileMetaData() to fpGetSubFileMetadataList(), KeyView reproduces the default and all metadata sets output by fpGetSubFileMetaData() in the output of fpGetSubFileMetadataList(). The default metadata set is output by fpGetSubFileMetaData() when the metaNameCount member of the KVGetSubFileMetaArgRec argument is set to 0, and the all metadata set is output when metaNameCount is set to -1. For each valid KVMetadataElem object metaElemOld in the default and all output of fpGetSubFileMetaData, the output of fpGetSubFileMetadataList() will contain a KVMetadataElement object metaElemNew such that metaElemNew.pKey contains the name in metaElemOld.strType, and metaElemNew.pValue contains the value represented by metaElemOld.data. Where KeyView can standardize the field represented by metaElemOld, the output of fpGetMetadataList also contains that standardized field.