  The new era of the Web is known as the semantic Web or the Web of data. The
semantic Web depends on ontologies that are seen as one of its pillars. The
bigger these ontologies, the greater their exploitation. However, when these
ontologies become too big other problems may appear, such as the complexity to
charge big files in memory, the time it needs to download such files and
especially the time it needs to make reasoning on them. We discuss in this
paper approaches for segmenting such big Web ontologies as well as its
usefulness. The segmentation method extracts from an existing ontology a
segment that represents a layer or a generation in the existing ontology; i.e.
a horizontally extraction. The extracted segment should be itself an ontology.
