The OpenGIS® Filter Encoding Standard (FES) defines an XML encoding for filter expressions. A filter expression logically combines constraints on the properties of a feature in order to identify a particular subset of features to be operated upon. For example, a subset of features might be identified to render them in a particular color or convert them into a user-specified format. Constraints can be specified on values of spatial, temporal and scalar properties. An example of a filter is: Find all the properties in Omstead County owned by Peter Vretanos. This standard is used by a number of OGC Web Services, including the Web Feature Service [http://www.opengeospatial.org/standards/wfs], the Catalogue Service [http://www.opengeospatial.org/standards/cat] and the Styled Layer Descriptor Standard [http://www.opengeospatial.org/standards/sld].