Glossary of Terms
Context: Unless otherwise stated, the context for all definitions is computer, data, or information science.
Source: Unless otherwise stated, the source of all definitions is Wikipedia
Graph concepts
Knowledge Graph
There are numerous definitions of knowledge graphs. One one the simpler definitions is: A digital structure that represents knowledge as concepts and the relationships between them (facts.) A knowledge graph can include an ontology that allows both humans and machines to understand and reason about its contents.
Graph database
A database that uses graph structures for semantic queries with nodes, edges, and properties to represent and store data. The edges form the graph. The graph relates the data items in the store to a collection of nodes and edges, the edges representing the relationships between the nodes. The relationships allow data in the store to be linked together directly and, in many cases, retrieved with one operation. Graph databases hold the relationships between data as a priority. Querying relationships is fast because they are perpetually stored in the database. Relationships can be intuitively visualized using graph databases, making them useful for heavily inter-connected data
Graph Structure
An abstract data type for implementing the graph theory concepts of Undirected and Directed graphs. The former concept consists of unordered pairs of vertices (also called nodes or points.) The latter consists of ordered pairs of vertices.
A graph data structure consists of a finite set of vertices, together with a set of unordered or ordered pairs of these vertices as defined above. These pairs are known as edges (also called links or lines, and sometimes called arrows or arcs for a directed graph.) The vertices may be part of the graph structure, or may be external entities represented by integer indices or references.
A graph data structure may also associate an edge value to each edge, such as a symbolic label or a numeric attribute (cost, capacity, length, etc.)
Directed Graph
A directed graph (or digraph) is a graph made up of vertices connected by directed edges often called arcs.
Ontology
A way of showing the properties of a subject area and how they are related, by defining a set of concepts and categories that represent the subject. An ontology encompasses a representation, formal naming and definition of the categories, properties and relations between the concepts, data and entities that substantiate one, many, or all domains of discourse.
Semantic Query
Semantic queries allow for queries and analytics of an associative and contextual nature. Semantic queries enable the retrieval of both explicitly and implicitly derived information based on syntactic, semantic and structural information contained in data. They are designed to deliver precise results (possibly the distinctive selection of one single piece of information) or to answer more fuzzy and wide-open questions through pattern matching and digital reasoning.
Node
A vertex (plural vertices) or node is the fundamental unit of which graphs are formed: an undirected graph consists of a set of vertices and a set of edges (unordered pairs of vertices), while a directed graph consists of a set of vertices and a set of arcs (ordered pairs of vertices). In a diagram of a graph, a vertex is usually represented by a circle with a label, and an edge is represented by a line or arrow extending from one vertex to another.
Edge
An edge (together with vertices) is one of the two basic units out of which graphs are constructed. Each edge has two (or in hypergraphs, more) vertices to which it is attached, called its endpoints. Edges may be directed or undirected; undirected edges are also called lines and directed edges are also called arcs or arrows. In an undirected simple graph, an edge may be represented as the set of its vertices, and in a directed simple graph it may be represented as an ordered pair of its vertices. An edge that connects vertices x and y is sometimes written xy.
Data
Delta Encoding
A way of storing and transmitting data in the form of deltas (differences) between sequential data rather than complete files; sometimes referred to as data differencing. Delta encoding is sometimes called delta compression, particularly where archival histories of changes are required, for example, in revision control systems such as GitHub and the TerminusDB version-controlled graph databases.
Metadata
Metadata is data that provides information about other data, but not the content of the data, such as the text of a message or an image. There are many distinct types of metadata.
RDF
The Resource Description Framework (RDF) is a family of W3C specifications used as a general method for conceptual description or modeling of information that is implemented in web resources, using a variety of syntax notations and data serialization formats.
Triple
A semantic triple, or RDF triple or simply triple, is the atomic data entity in the RDF data model. A triple is a set of three entities that codifies a statement about semantic data in the form of subject–predicate–object expressions. Examples:
Table: Subject-Predicate-Object examples
| Subject | Predicate | Object |
|---|---|---|
| Bob | knows | John |
| Bob | is | 35 |
This format enables knowledge to be represented in a machine-readable way. Every part of an RDF triple is individually addressable via unique URIs. For example, the statement "Bob knows John" might be represented in RDF as:
http://example.name#Bob12 http://xmlns.com/foaf/0.1/knows http://example.name#John34
Semantic Data
Semantic data or Semantic Data Model (SDM) is a high-level semantics-based database description or model. This database model is designed to capture more of the meaning of an application environment than is possible with contemporary database models.
Serialization
The process of translating a data structure or object state into a format that can be stored (for example, in a file or memory) or transmitted (for example, over a computer network) and reconstructed later (possibly in a different computer environment.)
Schema
The organization of data as a blueprint of how the database is constructed.
Attribute
The columns of a table in relational databases. Similar to properties in graph databases.
Entity
Tables in relational databases. Similar to nodes in graph databases.
Relationship
The relationships between two tables in relational databases. In graph databases, relationships are directed and named connections between two nodes.
TerminusDB specific
WOQL
WOQL (Web Object Query Language) is TerminusDB's query language for querying complex data patterns and structures. WOQL is based on three fundamental concepts: WOQL triples, WOQL variables and WOQL operators. WOQL also provides PCRE.
WOQL does not use the SPARQL protocol.
Immutable
In programming, the state of an immutable object is unchangeable, i.e., its state cannot be modified after it is created. In TerminusDB, immutable data means an instance of data that cannot be changed after it is created. Newer instances or versions of that data can be created, but the tat version is immutable.
Mutable
In contrast to an immutable object, a mutable object is changeable.
PCRE
Perl Compatible Regular Expressions (PCRE) is a library that implements a regular expression engine, inspired by the capabilities of the Perl programming language. PCRE's syntax is more powerful and flexible than many other regular-expression libraries.
IRI
The Internationalized Resource Identifier (IRI) is an internet protocol standard that builds on the Uniform Resource Identifier (URI) protocol by greatly expanding the set of permitted characters. IRIs extend URIs by using the Universal Character Set, where URIs were limited to ASCII, with far fewer characters. IRIs may be represented by a sequence of octets but by definition are defined as a sequence of characters, because IRIs may be spoken or written by hand.