Terminologies

Name	Description
GQL	Graph Query Language, another and the only standard data query language since SQL (Structured Query Language).
UQL	Ultipa Graph Query Language, a kind of GQL that can fully operate Ultipa Graph system.
Node	Represents the entity in the real world, it is also called 'vertex' in graph theory.
Edge	Represents the relation between entities in the real world. An edge connects a pair of nodes, all the edges in Ultipa Graph system are directed edge (see the term 'Direction' below). The edge connecting two identical nodes is a Loop.
Metadata	The general term of node and edge.
Path	A sequence with definite initial-node and terminal-node, alternating between nodes and edges. Nodes in path can correspond while edges cannot. The sequence of IDs of the nodes and edges in a path can be regarded as the unique identifier of the path.
Intermediate Node	The nodes in a path other than the initial-node and terminal-node.
Circle	When a node of a path corresponds with any other nodes in the path, the path is judged as 'has circle'. Please note on the exception of A-B query and Autonet query: Paths that have circle can be ruled out using parameter no_circle() in path query command so they will not be returned.
Shortest Path	If a path contains the least number of edges, at least one edge, to walk from its initial-node to terminal-node, it is called a shortest path of the specified initial-node and terminal-node. The 'least number of edges' should be understood as 'minimum sum of edge weights' in case of a weighted shortest path.
Graph	The dataset of nodes and edges, which is equivalent to a data collection of multiple paths that intersect. The smallest unit of graph is node, a graph is not necessarily connected.
Subgraph	A part of nodes and edges of a graph. The result of node query and path query can be considered as a subgraph.
GraphSet	Comprises the graph data (nodes and edges), along with graph model (definition of schemas and properties), property indexes, full-text indexes, engine indexes and algorithmic tasks created on the graph.
Graph System	Ultipa Graph HTAP System, a combination of graph computing engine, graph algorithm engine, full-text search engine and etc., built upon a server cluster. An Ultipa Graph system also contains GraphSets, users and policies, and the algorithm packages installed by the user.
Instance	Ultipa Graph system instances, that is, the running applications on Ultipa Server, each instance generally runs on one virtual or physical host, and multiple instances can form a cluster environment.
Schema	A schema of node or edge includes a set of properties that describes the structure and content of node or edge. Each node or edge can only belong to one schema.
Property	A property belongs to a schema and is used to describe a character of node or edge. There are system properties (see the term 'ID', 'FROM' and 'TO' below) and custom properties.
Graph Model	The definition of schemas and properties of a graph, it represents the application scenario a graph describes.
Property Index	The index created for property values and stored in the disk, to improve the query efficiency of metadata properties.
Full-text Index	The revert index created for the word-segmentation results of property values and stored in the disk, to improve the query efficiency for keywords against long strings. Ultipa self-developed full-text engine employs different dictionaries in order to optimize the word-segmentation for different datasets.
Engine Index	The property of index loaded to the computing engine (see the term 'LTE' below), to improve the efficiency of path query and deep graph traversal by reducing IO cost. The query efficiency is often increased by several orders of magnitude. Engine index is mandatory when executing inter-step comparison, inter-step filtering and calculating weighted shortest path.
Filter	Appears in parameters that represent nodes or edges in the query command, to filter nodes and edges during graph queries. Ultipa filter is essentially a logic tree, which uses conditional operators, logical operators and numeric operators to calculate operands and return True or False. Refer to the chapter Filter | Operator for details.
LTE	Load to Engine, load property to the computing engine, to create engine index.
UFE	Unload from Engine, remove property from the computing engine, to delete engine index.
Direction (In)	An edge pointing to node A from another node is called an "In" edge of node A, or an edge of node A in the inbound direction. It is written as either A<-- or -->A.
Direction (Out)	An edge pointing from node A to another node is called an "Out" edge of node A, or an edge of node A in the outbound direction. It is written as either A--> or <--A.
Direction (Left)	An edge in a given path that points from the latter node to the previous node is called "Left" edge. It is written as A<--B.
Direction (Right)	An edge in a given path that points from the previous node to the latter node is called "Right" edge. It is written as A-->B.
ID	A system property that represents the unique identifier of metadata. Includes _id of node that is string with maximum 128 bytes, and _uuid of node and edge that is uint64.
FROM	A system property that represents the ID of start node of edge. Includes _from and _from_uuid, namely the _id and _uuid of the start node.
TO	A system property that represents the ID of end node of edge. Includes _to and _to_uuid, namely the _id and _uuid of the end node.