In UQL, various values and types can be used to represent information within the graph database. Understanding these values and types is essential for effective query construction and data manipulation.

Graph Types

A graph type refers to the type of data retrieved from the database, which are nodes, edges and paths.

Property Types

A property type refers to the data type of the values of a property. Ultipa supports the following property types:

Constructed Value Types

A constructed value type is a data type comprising composite elements. UQL supports the following constructed type:

Result Types

A result type refers to the data type of the values returned by a query. Ultipa defines the following result types.

RESULT_TYPE_NODE

This query returns all the information of @Paper nodes:

find().nodes({@Paper}) as n
return n{*}

Data structure of n:

{
  "data": [
    {
      "id": "P2",
      "uuid": "8718971077612535835",
      "schema": "Paper",
      "values": {
        "title": "Optimizing Queries",
        "score": 9
      }
    },
    {
      "id": "P1",
      "uuid": "8791028671650463770",
      "schema": "Paper",
      "values": {
        "title": "Efficient Graph Search",
        "score": 6
      }
    }
  ],
  "alias": "n",
  "type": 2,
  "type_desc": "RESULT_TYPE_NODE"
}

RESULT_TYPE_EDGE

This query returns all the information of outgoing @Cites edges:

n().re({@Cites} as e).n()
return e{*}

Data structure of e:

{
  "data": [
    {
      "from": "P1",
      "to": "P2",
      "uuid": "1",
      "from_uuid": "8791028671650463770",
      "to_uuid": "8718971077612535835",
      "schema": "Cites",
      "values": {
        "weight": 2
      }
    }
  ],
  "alias": "e",
  "type": 3,
  "type_desc": "RESULT_TYPE_EDGE"
}

RESULT_TYPE_PATH

This query returns all the information of outgoing 1-step paths:

n().re().n() as p
return p{*}

Data structure of p:

{
  "data": [
    {
      "nodes": [
        {
          "id": "P1",
          "uuid": "8791028671650463770",
          "schema": "Paper",
          "values": {
            "title": "Efficient Graph Search",
            "score": 6
          }
        },
        {
          "id": "P2",
          "uuid": "8718971077612535835",
          "schema": "Paper",
          "values": {
            "title": "Optimizing Queries",
            "score": 9
          }
        }
      ],
      "edges": [
        {
          "from": "P1",
          "to": "P2",
          "uuid": "1",
          "from_uuid": "8791028671650463770",
          "to_uuid": "8718971077612535835",
          "schema": "Cites",
          "values": {
            "weight": 2
          }
        }
      ],
      "length": 1
    }
  ],
  "alias": "p",
  "type": 1,
  "type_desc": "RESULT_TYPE_PATH"
}

RESULT_TYPE_ATTR

This query returns the title property of @Paper nodes:

find().nodes({@Paper}) as n
return n.title

Data structure of n.title:

{
  "data": {
    "alias": "n.title",
    "type": 4,
    "type_desc": "RESULT_TYPE_ATTR",
    "values": [
      "Optimizing Queries",
      "Efficient Graph Search"
    ]
  },
  "alias": "n.title",
  "type": 4,
  "type_desc": "RESULT_TYPE_ATTR"
}

RESULT_TYPE_TABLE

This query returns a table:

find().nodes({@Paper}) as n
return table(n.title, n.score) as table

Data structure of table:

{
  "data": {
    "name": "table",
    "alias": "table",
    "headers": [
      "n.title",
      "n.score"
    ],
    "rows": [
      [
        "Optimizing Queries",
        "9"
      ],
      [
        "Efficient Graph Search",
        "6"
      ]
    ]
  },
  "alias": "table",
  "type": 5,
  "type_desc": "RESULT_TYPE_TABLE"
}

Null Value

The null value is a special value available in all nullable types. Any non-null value is a material value.

Null Scenarios

The null values can arise in various contexts, including:

• Default Assignment: When nodes or edges are inserted, nullable properties that lack specified values automatically receive null.
• Explicit Null Specification: During node or edge insertion, nullable properties can be intentionally set to null.
• Value Removal: Removing a property’s value replaces it with null.
• New Property Assignment: When adding a new property to a schema, any existing nodes or edges with that schema are assigned null for the new property by default.
• Nonexistent Property References: Referencing a property that does not exist returns null.
• Optional Matching: When the OPTIONAL keyword is used with some clauses (find(), khop(), etc.), if no result is found, the clause yields null instead of empty return.

Null in Comparisons

The null value is not comparable to any other value due to its inherently unknown nature. Consequently, comparisons involving null using normal operators such as = or > do not typically yield true or false but rather an unknown result, also represented by null.

Comparisons involving null require special handling with null predicates (IS NULL and IS NOT NULL).

Null Treatments

The null values receive special treatment in some contexts. For instance:

• Aggregate functions typically ignore null values.
• The GROUP BY clause groups all null values together.