If metadata is data about data, then
a metadata model is a system that allows the creation, editing, and
management of metadata. SharePoint has a metadata model—called the
Content Type Model.
The SharePoint Content Type Model consists of metadata types: content types,
which themselves consist of metadata fields; columns; and the
management of these types in the core of the SharePoint platform.
What are Content Types and Site Columns?
A SharePoint content type is a grouping of
fields that describe a data entity in the SharePoint site collection or
site, such as a document, calendar event, task, or any other list item.
Each content type consists of one or multiple fields, better known as
columns.
Content types exist at either the root site
collection or subsite level. Lower sites in the hierarchy may use
content types from parent sites to define data elements. In both cases,
content types reside in the Content Type Gallery of the site or site
collection.
The fields of content types exist as centrally managed site columns,
at the same level as the containing content type or at parent levels to
it. For example, a content type defined at a subsite level may contain
site columns that reside in the root site collection or parent site in
the hierarchy. Sites may not leverage content types and site columns at
lower subsite levels than the current site—just up the hierarchy chain.
There is a difference between centrally managed
site columns and list columns. When creating a custom list, the user
may define columns specifically for the new list, meaning the columns
bind only to that list. By contrast, site columns reside in the Site
Column Gallery, and users may reuse these columns in lists (add an
existing column) and content types.
Content types may inherit from other content
types at the same level in the site hierarchy or a parent level. Even
the most basic content types at least inherit from the stock Item
content type, which contains the Title site column. Through
inheritance, users may customize content types by defining new types
that have the same columns as the parent, with additional columns to
complete the specialization. For example, if you want to customize task
list items with new columns, rather than creating a new content type,
you can inherit the existing Task content type and add the new custom
columns. Inheritance provides the added benefit that any changes to a
parent content type apply to content subtypes.
Note Never change stock content types and site columns; always inherit from content types, and then specialize.
New Content Type Model Functionality
SharePoint has included lists, libraries,
content types, site columns, and list columns since SharePoint 2007.
However, each version of SharePoint has brought change to content
types. Following are some of the more noteworthy features, beyond the
basic content type behavior (described previously). Microsoft
introduced many of the following features in SharePoint 2010, which of
course also exist in SharePoint 2013.
- Content types and lists that use lookup site columns may specify
additional columns of the lookup list to include, in addition to the
primary lookup column.
- SharePoint includes referential integrity in lookup columns. For
example, when you delete a list item from a list, referenced by a
lookup column, SharePoint will delete the dependent list item, prevent
the deletion of the parent, or do nothing, depending on a referential
integrity setting.
- Document sets (a special content type) allow collection of
documents in one list item. They are ideal for collecting multiple
documents that combine to a single finished entity, such as a proposal.
- A Managed Metadata column type that maps to term sets in the Managed Metadata Service Term Store exists.
- An Enterprise Keywords column allows users to add their own tags (folksonomy) as part of the Managed Metadata Service.
- Since SharePoint 2010, users can now share content types across site collections via a centralized content type hub.
- SharePoint includes columns and content types to access external data via the Business Connectivity Service.
- SharePoint includes a Rating site column.
- Since SharePoint 2010, SharePoint includes advanced routing of documents via Content Organizer and policy rules.
