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FEKL Query Concepts

There are three types of concept to use when creating a FactEngine statement:

- ModelElementName;
- Predicate
- PropertyNodeIdentification

ModelElementName

When querying a database Model Elements are commensurate to Tables, Nodes and Attributes in your database.

- Entity Relationship Diagrams have Entity and Attribute model elements.
- Property Graph Schemas have Node and Property model elements.

Schemas created using Fact-Based Modeling, as used by FactEngine, consist of model elements, such as Entity Types, Value Types and Objectified Fact Types. Role Constraints and Roles, for instance, are also model elements.

So when querying a database you relate the model elements in your conceptual models in FactEngine/Boston to their corresponding model elements within your database. The name of each model element is called a ModelElementName within the syntax descriptions in this documentation. For example, the following FactEngine query has Lecturer, Room, Position, School and Faculty as ModelElementNames.

Suffixes

Note that each ModelElementName can have a suffix, such as in "2" in "Issue 2" as in the following query:

Predicates

As the name suggests, Predicates are the predicates of your conceptual models in Boston.

The query above has the following predicates;

- occupies
- holds
- is in
- works for

Property Node Identification

If you need to identify a particular data item in your database you do that with a PropertyNodeIdentification clause.

In the example query above, (Faculty:'IT') finds a particular row/node in your database that is uniquely identified by the name, 'IT', and where the first unique index of the node/table is used to find the appropriate attribute/property value.

FactEngine Query Language has three standard comparators, Equals, Not Equals and LIKE.

They are implemented as part of the syntax for Property Node Identification.

Equals comparator

The colon, :, is used for equals.

Not Equal/s comparator

The bang, !, symbol is used for Not Equals.

LIKE comparator

The tilde, ~, symbol is used for the LIKE comparator.