PDFlib TET PDF IFilter 4.0 Manual

3.5 Multivalued Properties
Metadata properties can contain one or more values. Single-valued properties consist of a
flat value which describes the document as a whole. Examples for single-valued properties
are the creation date (property sources: xmp:CreateDate and /Info/CreationDate) and
the unique document identifier (dc:identifier).
Multivalued properties may occur more than once per document. Examples for multivalued
properties are the list of document authors and document keywords. The multiplicity
of a property may have several reasons:
> The source of the property is an XMP container type and can therefore hold multiple
entries at once, e.g. dc:creator has type Seq in XMP.
> The property is populated from a multivalued pCOS path with wildcards, where the
wildcards will be expanded to any number of individual entries, e.g. bookmarks[*]/
Title.
> The property is populated from more than one source, and the precedence attribute
of the property has the value try-all, e.g. pdf:Keywords and /Info/Keywords. However,
the default precedence=first-wins processes only the first non-empty property source.
Vector treatment of properties. By default, TET PDF IFilter will process all relevant
sources in the property definition (subject to the precedence attribute), and emit as
many non-empty property values as are available. In other words, each value will be returned
as a single entity to the IFilter client. Property values will be returned in unspecified
order.
Alternatively, multivalued properties can be provided as vectors to the IFilter client.
This means that a single array entity will be emitted which can hold one or more values.
There are several relevant aspects of vector processing for properties:
> SharePoint supports multivalued properties only if they are processed as vector entities.
> Some IFilter clients, e.g. Windows Search, support vector queries where you can
search for one or more values in a multivalued vector property in a single query.
> Indexing Service supports vectors only for properties with type String.
Keep in mind that there are two separate concepts: multivalued refers to an aspect of the
property’s source, while vector processing refers to the way in which property values are
transferred to the IFilter client. Vector processing can be applied to multivalued properties
even if they contain only a single value.
Some of the predefined properties are multi-valued (see Appendix A, »Predefined
Metadata Properties«).
XML configuration for vector properties. Vector processing for custom properties can
be enabled with the emitAsVector attribute of the Property element:
44 Chapter 3: Metadata Properties