This glossary provides basic definitions for important Freebase terms. For more detailed information, follow the links associated with the terms. Send suggestions for terms to include, or definitions, to phil@metaweb.com. 

Blob

Any block of binary data uploaded via the trans/upload or trans/uri_submit services only. All uploaded images, files, and URLs are blobs.

Blurbs

The first "n" characters (up to a maximum number) of text/* type blobs requested by the trans/blurb service.

Co-type 

A co-type refers to an additional type that is added to a topic. For example, the topic Ernest Hemingway is co-typed Person, Deceased Person, Film Writer, Author,  Award Winner, and Influence Node. Note that there is no inheritance between these types, meaning that the  properties associated with one type are not added to the other types.

Compound Value Type (CVT)

A compound value type (CVT) is an element that ties together properties from several types. Typically (and trickily) a compound value type doesn't have a display name because it is only a container object for a group of properties. For example, the CVT Musical Group Membership contains the name of a band, the name of the musician, and the role or instrument played. This data will appear on the related topic instances of Musical Artist even though the properties exist within the compound value type. This is because Musical Group Membership is a CVT and is the expected type for a property (Members) on Musical Artist.

Disambiguator 

In a type schema, properties can be set to Display as Disambiguator. The Film type, for example, has an Initial Release Date property that is set as a disambiguator. This means on any topic that displays films, the film's name will be paired with its Initial Release Date. For example, Loverboy is a film directed by Kevin Bacon. When Loverboy is listed as one of the films directed by Kevin Bacon in his biographical topic, the initial release date is displayed next to it. 

Domain

A domain is a collection of types. This arrangement can be counterintuitive, because in many databases, a domain (or a similar element) would be a collection of topics. To get a sense of the Freebase approach, check out the Film domain, which lists its types, including Film Actor, Film Genre, Film Director and so forth. Those types then contain topics like Salma Hayek, Romantic Comedy, and Quentin Tarantino. For more information, check out the Domains topic.

Enumerated Type

An object of /type/enumeration that has a specified enumeration namespace. For each instance of the enumerated type, MQL creates a unique identifier, or key, in the enumerated namespace. Enumerated types allow you to refer to instances of the type easily by key value. For example, for the enumerated type /people/gender, whose enumeration namespace is /topic/en, the instances male and female may easily be referred to by the keys /topic/en/male and /topic/en/female.

Enumeration

An enumeration is a namespace in which MQL creates human-readable unique indentifiers for instances. This identifier can be used as a foreign key to simplify reconciliation between Freebase and other datasets, provides a way to access Freebase topics without needing to reference the Globally Unique Identifier (GUID), and enforces uniqueness among Freebase topics. An example of enumeration would be the NCBI Taxon ID, where the number 9233 refers to the Emperor Penguin.

Globally Unique Identifier (GUID)

A unique numerical identifier assigned to every Freebase topic and to primitives. The GUID for this topic, for example, is 9202a8c04000641f800000000830e5c0.

Graph (or The Graph)

Freebase is a graph database. This means that instead of using tables and keys found in conventional database to define data structures, Freebase defines its data structure as a set of nodes and a set of links that establish relationships between the nodes. Because its data structure is non-hierarchical, Freebase can model much more complex relationships between individual elements than a conventional database, and is open for users to enter new objects and relationships into the underlying graph.

Phylogeny Pattern

A hierarchical or sequential classification system that proceeds from the specific to the general by means of parent/child relationships for the objects being classified. An example would be the biological progression from species to Kingdom through Phylum, Class, Order, etc., or the parents/children pair associated with a person. 

Primitive

The fundamental unit of graph storage, A primitive represents a single object (without its properties) or a single property (a link, possibly with an associated text string or number).  A primitive generally corresponds to a basic fact stored in the database, such as the name of a topic or a person's date of birth. The developer's toolbar provides an "Explore View" that can be used to browse the primitive structure of the database.  Freebase currently enforces a default write limit of 10,000 primitives per day per user.

Primitive Type 

A basic data construct of  the Metaweb Query Language (MQL). It refers to basic forms of data such as strings or numbers from which more complex notions, such as "Name," "Film," or "Person," are constructed.

Property  

In Freebase, a property is an element of a type. For example, the Person type includes properties such as Birthplace, Birth Date, Parents, and Country of Nationality. For more information, check out the Properties topic.

Reciprocal Property 

A reciprocal property is one that is linked to a similar property in another type. When information for one of those properties  is  entered for a Freebase topic, that topic is automatically linked as  an entry  for the reciprocal property. For example, if the Films Directed property in the Film Director type is linked to the Film Director property in the Film type, then entering  a director's name for the Film Director property in a Film topic will cause the  film’s name to  be entered in the Films Directed property for that director's topic.

 Schema 

A schema generally refers to an organizational pattern or structure, often represented as a diagram. In Freebase, schema refers to the collection of properties that make up a type, along with additional information about those properties. When viewing any type, click View Schema on the More Options menu below the type name to see this information. 

Topics

Topics represent things in the world that we like to talk about--people, places, things or ideas. Examples include: “United States”, “Grover Cleveland”, “Apple iPod Nano”, “1600 Pennsylvania Ave NW, Washington DC” or “Lyle Lovett.” In Freebase, topics are tied to types, and each type is made up of  elements called properties. For more information, check out the Topics topic.

Transaction ID (TID or Txn ID)

An HTTP response header that is returned with each request to Freebase.com that uniquely identifies that request. If a request causes an error or other unexpected result, the TID can be used to review the activity for that request. 

Types  

A type is a collection of related properties. For example, the Person type includes properties like Birthplace, Birth Date, Parents, and Country of Nationality. For more information, check out the Types topic.