Cypher Support

This document outlines the current capabilities of GIE in supporting Neo4j’s Cypher queries and compares them to the syntax specified in Neo4j. While our goal is to comply with Neo4j’s syntax, GIE currently has some limitations. One major constraint is that we solely support the read path in Cypher. Therefore, functionalities associated with writing, such as adding vertices/edges or modifying their properties, remain unaddressed.

We provide in-depth details regarding Cypher’s support in GIE, mainly including data types, operators and clauses. We further highlight planned features that we intend to offer in the near future. While all terminologies, including data types, operators, and keywords in clauses, are case-insensitive in this document, we use capital and lowercase letters for the terminologies of Neo4j and GIE, respectively, to ensure clarity.

Data Types

As Neo4j, we have provided support for data value of types in the categories of property, structural and constructed. However, the specific data types that we support are slightly modified from those in Cypher to ensure compatibility with our storage system. Further details will be elaborated upon.

Property Types

The available data types stored in the vertices (equivalent of nodes in Cypher) and edges (equivalent of relationships in Cypher), known as property types, are divided into several categories including Boolean, Integer, Float, String, Bytes, Placeholder and Temporal. These property types are extensively utilized and can be commonly utilized in queries and as parameters – making them the most commonly used data types.

Category	Cypher Type	GIE Type	Supported	Todo
Boolean	BOOLEAN	bool
Integer	INTEGER	int32/uint32/int64/uint64
Float	FLOAT	float/double
String	STRING	string
Bytes	BYTE_ARRAY	bytes
Placeholder	NULL	none		Planned
Temporal	DATE	date		Planned
Temporal	DATETIME (ZONED)	datetime (Zoned)		Planned
Temporal	TIME (ZONED)	time (Zoned)		Planned

Structural types

In a graph, Structural Types are the first-class citizens and are comprised of the following:

• Vertex: It encodes the information of a particular vertex in the graph. The information includes the id, label, and a map of properties. However, it is essential to note that multiple labels in a vertex are currently unsupported in GIE.

• Edge: It encodes the information of a particular edge in the graph. The information comprises the id, edge label, a map of properties, and a pair of vertex ids that refer to source/destination vertices.

• Path: It encodes the alternating sequence of vertices and conceivably edges while traversing the graph.

Category	Cypher Type	GIE Type	Supported	Todo
Graph	NODE	vertex
Graph	RELATIONSHIP	edge
Graph	PATH	path

Constructed Types

Constructed types mainly include the categories of Array and Map.

Category	Cypher Type	GIE Type	Supported	Todo
Array	LIST<INNER_TYPE>	int32/int64/double/string/pair Array
Map	MAP	N/A		only used in Vertex/Edge

Operators

We list GIE’s support of the operators in the categories of Aggregation, Property, Mathematical, Comparison, String and Boolean. Examples and functionalities of these operators are the same as in Neo4j. Note that some Aggregator operators, such as max(), we listed here are implemented in Neo4j as functions. We have not introduced functions at this moment.

Category	Description	Cypher Operation	GIE Operation	Supported	Todo
Aggregate	Average value	AVG()	avg()
Aggregate	Minimum value	MIN()	min()
Aggregate	Maximum value	MAX()	max()
Aggregate	Count the elements	COUNT()	count()
Aggregate	Count the distinct elements	COUNT(DISTINCT)	count(distinct)
Aggregate	Summarize the value	SUM()	sum()
Aggregate	Collect into a list	COLLECT()	collect()
Aggregate	Collect into a set	COLLECT(DISTINCT)	collect(distinct)
Property	Get property of a vertex/edge	[N|R].“KEY”	[v|e].“key”
Mathematical	Addition	+	+
Mathematical	Subtraction	-	-
Mathematical	Multiplication	*	*
Mathematical	Division	/	/
Mathematical	Modulo division	%	%
Mathematical	Exponentiation	^	power(a, b)
Temporal Mathematical	Add a duration to a temporal type	<temporal> + <duration>	<temporal> + <duration>
Temporal Mathematical	Subtract a duration from a temporal type	<temporal> - <duration>	<temporal> - <duration>
Temporal Mathematical	Subtract two temporal types, returning a duration in milliseconds	<temporal> - <temporal>	<temporal> - <temporal>
Temporal Mathematical	Add two durations	<duration> + <duration>	<duration> + <duration>
Temporal Mathematical	Subtract two durations	<duration> - <duration>	<duration> - <duration>
Temporal Mathematical	Multiply a duration by a numeric value	<duration> * <numeric>	<duration> * <numeric>
Temporal Mathematical	Divide a duration by a numeric value	<duration> / <numeric>	<duration> / <numeric>
Comparison	Equality	=	=
Comparison	Inequality	<>	<>
Comparison	Less than	<	<
Comparison	Less than or equal	<=	<=
Comparison	Greater than	>	>
Comparison	Greater than or equal	>=	>=
Comparison	Verify as NULL	IS NULL	is null
Comparison	Verify as NOT NULL	IS NOT NULL	is not null
Comparison	Perform case-sensitive matching on the beginning of a string	STARTS WITH	starts with
Comparison	Perform case-sensitive matching on the ending of a string	ENDS WITH	ends with
Comparison	Perform case-sensitive matching regardless of location within a string	CONTAINS	contains
Boolean	Conjunction	AND	and
Boolean	Disjunction	OR	or
Boolean	Exclusive Disjunction	XOR	xor		planned
Boolean	Negation	NOT	not
BitOpr	Bit and	via function	&
BitOpr	Bit or	via function	|
Boolean	Bit xor	via function	^
BitOpr	Bit reverse	via function	~		planned
BitOpr	Bit left shift	via function	<<
BitOpr	Bit right shift	via function	>>
Branch	Use with Project and Return	CASE WHEN	CASE WHEN		planned
Scalar	Returns the length of a path	length()	length()
ListLiteral	Fold expressions into a single list	[]	[]
MapLiteral	Fold expressions with keys into a single map	{}	{}
Labels	Get label name of a vertex type	labels()	labels()
elementId	Get a vertex or an edge identifier, unique by an object type and a database	elementId()	elementId()
Type	Get label name of an edge type	type()	type()
Extract	Get interval value from a temporal type	<temporal>.<interval>	<temporal>.<interval>
User Defined Functions	get all edges from a path	relationships(path)	gs.function.relationships(path)
User Defined Functions	get all nodes from a path	nodes(path)	gs.function.nodes(path)
User Defined Functions	get start node from an edge	startNode(edge)	gs.function.startNode(edge)
User Defined Functions	get end node from an edge	endNode(edge)	gs.function.endNode(edge)
User Defined Functions	convert integer value to datetime	datetime(1287230400000)	gs.function.datetime(1287230400000)
Path Modifier	get any shortest path between two endpoints	SHORTEST	SHORTESTPATH
Path Modifier	get all shortest paths between two endpoints	ALL SHORTEST	ALL SHORTESTPATH

Clause

A notable limitation for now is that we do not allow specifying multiple MATCH clauses in one query. For example, the following code will not compile:

MATCH (a) -[]-> (b)
WITH a, b
MATCH (a) -[]-> () -[]-> (b)  # second MATCH clause
RETURN a, b;

Besides, we support OPTIONAL MATCH. For example, the following query can be supported:

MATCH (a) -[]-> (b)
Optional MATCH (b) -[]-> (c) 
RETURN a, b, c;

Keyword	Comments	Supported	Todo
MATCH	only one Match clause is allowed
OPTIONAL MATCH	implements as left outer join
RETURN … [AS]
WITH … [AS]	project, aggregate, distinct
WHERE
WHERE NOT EXIST (an edge/path)	implements as anti join
ORDER BY
LIMIT
UNFOLD	The operation is similar to SQL’s ‘UNSET’, as it unfolds elements from a collection type

Additionally, we support two types of procedure call invocations in Cypher:

• We offer a set of built-in procedures that can be invoked directly within Cypher queries. These procedures are all prefixed with gs.procedure..

  Keyword	Comments	Example
  CALL	Retrieve schema information in a JSON format following the FLEX specification	call gs.procedure.meta.schema();
  CALL	Retrieve statistics information in a JSON format following the FLEX specification	call gs.procedure.meta.statistics();

• User-defined procedures: Users can define custom procedures in GIE and invoke them within their Cypher queries.