The Semantic Web as many very valuable potential use cases. Basically it is about how to
handle knowledge in the
ever increasing amount of data.
Ontology Engineering is a central application of the Semantic Web and is about how to design Ontologies (Ontology Design) as well as how to connect different Ontologies that might mean the same or might express the same (i.e. Ontology Mapping and Ontology Alignment).
Of course in the World there not just Ontologies. In fact most of knowledge that we have is expressed implicitly in our Natural language. So what we are dealing with is text and somehow we must come up with a way to represent text or to map text to Semantic Entities.
Names Entity Recognition (Named Entity Mapping) is the process to come from text to knowledge.
The Semantic Web today is a
Linked Open Data Cloud(Linked Data), which is basically nothing else than a kind of huge distributed Database of vocabularies and formally structured data that are represented in terms of RDF and are interoperable as they are formulated in RDF and are grounded, mapped and based on Ontologies and are interlinked. This is a huge Web of Data that consists of billions of facts which can be accessed. It enables to build simple Applications (Meshup Applications) that dynamically from the Content of the Web of Data create new websites with information that is really extremely useful and that would be difficult to achieve in the traditional way, but rather simple if using Semantic Web Technologies.
How to find things? Of course Semantics can support traditional Information Retrieval like Search Engines.
Semantic Search enables us to yield more precise and more complete search results compared to traditional information Retrieval Systems.