  Scholars have made handwritten notes and comments in books and manuscripts
for centuries. Today's blogs and news sites typically invite users to express
their opinions on the published content; URLs allow web resources to be shared
with accompanying annotations and comments using third-party services like
Twitter or Facebook. These contributions have until recently been constrained
within specific services, making them second-class citizens of the Web.
  Web Annotations are now emerging as fully independent Linked Data in their
own right, no longer restricted to plain textual comments in application silos.
Annotations can now range from bookmarks and comments, to fine-grained
annotations of a selection of, for example, a section of a frame within a video
stream. Technologies and standards now exist to create, publish, syndicate,
mash-up and consume, finely targeted, semantically rich digital annotations on
practically any content, as first-class Web citizens. This development is being
driven by the need for collaboration and annotation reuse amongst domain
researchers, computer scientists, scientific publishers, and scholarly content
databases.
