Hierarchy bridge entity

A hierarchy bridge entity is used to support dimensions that are subject to a ragged hierarchy. A ragged hierarchy is a hierarchy with an unbalanced and arbitrarily deep structure that usually cannot be described in advance of loading the data.

A ragged hierarchy is sometimes referred to as a variable depth hierarchy and the hierarchy bridge entity as a helper entity. A hierarchy bridge entity contains one instance for each separate path from each node in the hierarchical tree to itself, and to every node below it.

The hierarchy bridge entity is a special type of bridge entity.

Properties

Name (mandatory)

A textual name that identifies this hierarchy bridge entity in title case (all words start with a capital letter). This name is based on the name of the dimension entity that is subject to the ragged hierarchy. The name is suffixed with Hierarchy Bridge.

e.g. hierarchy bridge entity Involved Party Hierarchy Bridge

Dimensional type (mandatory)

The dimensional type is set to Bridge for all hierarchy bridge entities.

Owning package (mandatory)

The owning package to which this hierarchy bridge entity belongs.

e.g. package Location owns hierarchy bridge entity Geographic Area Hierarchy Bridge

Description (mandatory)

A complete and unambiguous description of this hierarchy bridge entity. This description must be as precise as possible. For example, a hierarchy bridge entity can support one or more types of hierarchies, in which case the description must mention the scope of the hierarchy bridge entity.

Persistent (mandatory)

A flag that indicates whether the entity is persistent or not. All entities of the delivered model are set to persistent. When the persistent flag is enabled, the entity is included in the scope of the practitioner, project, or enterprise data model.

Note: a persistent entity is physically implemented when it transforms the logical data model into a physical data model. When harvesting the data model, special care must be taken in connection with the persistent flag. For example, project A can decide to include an entity, but project B can decide not to include it. When harvesting project A at the enterprise level, the entity is set to persistent, indicating that the entity is part of the enterprise data model. Afterward, when harvesting project B at the enterprise level, care must be taken to keep the entity as persistent, although project B does not include it.

Basic attributes (optional)

One or more basic attributes describing this hierarchy bridge entity. These basic attributes may be based on the business terms that they originate from and may be dependent on their corresponding attributes in the Atomic Warehouse Model. A specific basic attribute that is held by most hierarchy bridge entities is the Hierarchy Code attribute, which describes the type of hierarchy that links the left and right dimensions.

e.g. attribute Hierarchy Code describes hierarchy bridge entity Involved Party Hierarchy Bridge

Unique identifier (mandatory)

An attribute that identifies uniquely and without business meaning the hierarchy bridge entity. By convention, the name is the name of the hierarchy bridge entity, which is suffixed with Id. This sole attribute defines the surrogate primary key of this hierarchy bridge entity. Natural keys, which can be useful in business reporting, are designed as basic attributes.

Ragged hierarchy basic attributes (mandatory)

Mandatory, basic attributes that enable navigation within the ragged hierarchy that is supported by this hierarchy bridge entity. These attributes are grouped in the Bridge Hierarchy attribute group.

Depth From Ancestor: An attribute that indicates the number of levels the descendant node is below the ancestor node. For example, a depth of 1 identifies all the immediate children of the ancestor for the given hierarchy. Combined with the Topmost Flag, the Depth From Ancestor indicates the hierarchy level in a top-down approach.
Topmost Flag: An attribute that indicates whether the ancestor node has no further nodes above it, meaning that it is the top of the hierarchy.
Lowest Flag: An attribute that indicates whether the descendant node has no further nodes beneath it, meaning that it is a leaf node of the hierarchy.

Note: standard query tools can be used to analyze the hierarchical structure via the hierarchy bridge table and to correctly summarize measures of the fact table. The hierarchy bridge table is joined to the fact table and to the dimension table for analysis. If the value for Depth From Ancestor is equal to 1, only the immediate descendants of the directly constrained dimension will be summarized. If the Lowest Flag is true, then only the lowest descendants of the directly constrained dimension will be summarized.

Primary key (mandatory)

The primary key uniquely identifies an instance of this hierarchy bridge entity and is composed of the unique identifier attribute. By convention, the name of the primary key is the name of the hierarchy bridge entity, which is suffixed with PK.

e.g. primary key Involved Party Hierarchy Bridge PK is the primary key of hierarchy bridge entity Involved Party Hierarchy Bridge

History Support attributes (optional)

Bridge History Support is an attribute group that holds all the technical attributes required to handle history management for bridge entities. Bridge History Support is defined on all hierarchy bridge entities.

Current Row Indicator (mandatory)

An attribute that indicates whether the version represents the current values in the business reality. It eases model consumability by allowing the business user to immediately identify, among all history versions of an instance, which row represents the current values in the business reality, without having to use a more complex condition on the Effective From Timestamp and Effective To Timestamp in their query. For example, this attribute is particularly useful for current and ad hoc analysis on dimensions without traversing fact tables.

Although the Current Row Indicator can be defined as a true/false Boolean attribute, it is recommended to use two more explicit values: Current and Not current.

Note: Not current is a better value than Expired, because rows may be created with values that will only become true in the business reality in the future.

e.g. attribute Current Row Indicator in hierarchy bridge entity Involved Party Hierarchy Bridge

Business transaction timestamps (mandatory)

Business transaction timestamps indicate the period during which the values of all attributes of the hierarchy bridge entity instance are true in the business reality:

Effective From Timestamp - The transaction time that represents the beginning of the time period during which the values of this recorded data are true in the business reality.
Effective To Timestamp - The transaction time that represents the end of the time period during which the values of this recorded data are true in the business reality.

These timestamps can be equivalent to the timestamps of the recording in the source system (system transaction timestamps) or can be different when the data is recorded before or after it is effective in the business reality.

System transaction timestamps (mandatory)

System transaction timestamps indicate the period during which the values of all attributes of the hierarchy bridge entity are true in the source system:

Valid From Timestamp - The transaction time that represents the beginning of the time period during which the values of this recorded data are true in the source system.
Valid To Timestamp - The transaction time that represents the end of the time period during which the values of this recorded data are true in the source system.

There is no overlap between the periods of versions of the same hierarchy bridge entity.

Population information attributes (optional)

Bridge Population Info is an attribute group that holds all the technical attributes regarding the population cycle of the hierarchy bridge entity. Those attributes assure a proper traceability between each instance of a hierarchy bridge entity and either the Atomic Warehouse element, or the source system element, from which it is populated. Bridge Population Info is defined on all hierarchy bridge entities.

Population Description: An attribute that provides textual information about the population cycle.
Population Timestamp: An attribute that holds the timestamp of the population cycle.
Source System Code: An attribute that holds the code of the application or source system from which the entity instance was populated.
Source System Name: An attribute that holds the name of the application or source system from which the entity instance was populated.
Source System Unique Id: An attribute that holds the source system's unique identifier of the information that is used to populate the entity instance.

Relationships (optional)

The relationships to other entities. The hierarchy bridge entity is related to one or no dimension entity. When a primary key component of a bridge entity may represent more than one dimension entity, then the relationship is implicit and the foreign key is defined as a soft link.

Note: a hierarchy bridge entity may also be attached directly to a fact entity.

e.g. dimension entity Geographic Area Dimension is parent of relationship is parent of / has for parent with hierarchy bridge entity Geographic Area Hierarchy Bridge
e.g. dimension entity Geographic Area Dimension is parent of relationship is child of / has for child with hierarchy bridge entity Geographic Area Hierarchy Bridge

Originating Atomic Warehouse Model elements (mandatory)

One or more dependencies to the Atomic Warehouse Model elements from which this hierarchy bridge entity originates. This indicates from which Atomic Warehouse Model entity, the hierarchy bridge entity is populated, in an environment where the Atomic Warehouse is deployed. By convention, the name of the dependency is AWM - Data Model Mapping and the dependency type is Data Model Mapping.

e.g. hierarchy bridge entity Geographic Area Hierarchy Bridge has a population dependency to the target Atomic Warehouse Model entity Location Navigation
e.g. hierarchy bridge entity Involved Party Hierarchy Bridge has a population dependency to the target Atomic Warehouse Model entity Involved Party Navigation