Link_HK

Applies to
Platform: Microsoft SQL Server · Snowflake · Snowflake dbt · Databricks · Databricks dbt · Fabric Lakehouse · Fabric Warehouse · Oracle
Architecture: Data Vault

Link_HK is the hash key that identifies a relationship between business keys in a Link. Link Satellites carry the same value to reference their Link.

Objects that carry it

Link, Driving Key Link, Hierarchical Link, Same As Link and their Business Vault counterparts: the identity and primary key of the table.
Link Satellite, Effectivity Link Satellite, Record Tracking Link Satellite, Non-Historized Link Satellite and their Business Vault counterparts: the reference to the Link.

Every object of these types gets the term when it is created. The generator calculates the value, so you do not map it; you can change its data type in Manage Default Terms.

Value

The Hashing view hashes the business-key terms of the Link in their term order, with the project Hash Algorithm. These are the foreign-key terms that reference the Hubs, plus business keys of the Link itself. A Link Satellite hashes its foreign-key terms in the term order of the Link, so it gets the same value as the Link. How the values are prepared and joined is explained in How biGENIUS-X builds hash values.

The Link also stores one hash per referenced Hub, see DVLINK_ForeignKey_Identity. The unknown-member row has a Link_HK that consists of zero bytes only.

Data type

Platform	Type
Microsoft SQL Server	`binary(20)`
Fabric Warehouse	`varbinary(20)`
Oracle	`RAW(20)`
Snowflake, Snowflake dbt	`BINARY(32)`
Databricks, Databricks dbt, Fabric Lakehouse	`binary`

The data type must match the length of the selected Hash Algorithm.

Example

A Driving Key Link on Microsoft SQL Server references an employee Hub and a job function Hub through EMPLOYEE_ID and JOBFUNCTION_ID. Its Hashing view calculates:

CAST(HASHBYTES('SHA1', CAST('' AS VARCHAR(MAX))
    + ISNULL(CAST([FK_common_employee_EMPLOYEE_EMPLOYEE_ID]
        AS NVARCHAR(4000)), N'_NULL_')
    + N'_'
    + ISNULL(CAST([FK_common_jobfunction_jobfunction_JOBFUNCTION_ID]
        AS NVARCHAR(4000)), N'_NULL_'))
    AS VARBINARY(20)) AS [Link_HK]

Employee 7 changes from job function 2 to 4 in the second load, so the Link gets a second row:

EMPLOYEE_ID  JOBFUNCTION_ID  Link_HK
7            2               0xCCF7607B8C8266232B829A18F7B19491133528CA
7            4               0xCCE46EF3F5DEAE3CAD8A12429B720FBC810F0116
8            3               0x53E79910417D737A7645D6C925FF1D0D568B4810

Release differences

Generator 2.4: Snowflake uses SHA2-256 with BINARY(32) by default. Up to Generator 2.3 the default was HASH with a numeric type, see Generators Release - 2.4.0.
Generator 2.2: Databricks and Fabric Lakehouse store hash values as binary. Up to Generator 2.0 they were string.

Reference: Hash Algorithm (Project), Hub_HK, DVLINK_ForeignKey_Identity, DrivingKeyLink_HK
See also: How biGENIUS-X builds hash values, Create a Link, Create a Link Satellite