Draft:Hub Star Modeling

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Hub Star Modeling is a database modeling method specialized for data integration. It simplifies the integration of reference data, master data, and transactional data in data warehouses and data lakehouses. This method was introduced by Shahram Salami in 2024 [1].

Star Relationships

Main Components
Hub Star comprises two main components: hubs, which integrate entities from different data sources, and stars, which represent the data in relationships between these hubs.

Hubs
Hubs are classified into three types: domain hubs, reference hubs, and virtual hubs, which represent master data, reference data, and transactional data:

• Domain hubs abstractly define master data and transactional data by their business keys.
• Reference hubs define reference data with their business keys and descriptive attributes.
• Virtual hubs, including Time hub and Item hub, are not explicitly defined in the model but their keys are used in the star tables. The Time hub contains all timestamps, while the Item hub contains partial keys for week entities that lack independent business keys.

The following table represents the structure of domain and reference hubs:

Hub Struture

Attribute	Description	Applicable Hubs
LoadSoure	Metadata/ The loading source	Domain and Reference
ChangeTS	Metadata/ The record change/create timestamp in the source	Domain and Reference
LoadTS	Metadata/ The record load timestamp in the hub	Domain and Reference
Hub Key	A special simple (non-composite) surrogate key that can be generated by the system (as auto-increment) or be computed over business keys (using functions such as concatenation, hashes, or numeric casts)	Domain and Reference
Global/ Local Business Key	One of the entity natural keys, which is immutable, mandatory, and either unique globally or locally within each data source	Domain and Reference
Descriptives	Optional descriptive attributes including hub keys of other reference hubs	Reference

Stars
Stars represent the data in relationship between hubs. Depending on the implementation, stars are classified as either mutable or append-only stars. Some metadata are only supported in mutable stars. Stars have the following structure:

Star Structure

Attribute	Description	Applicable Stars
LoadSource	Metadata/ The loading source	All
ChangeTS	Metadata/ The source change/create timestamp of the record	All
LoadTS	Metadata/ The load timestamp of the record	All
IsDeleted	Metadata/ Has a true value if a delete operation expires the row	All
ChangeEndTS	Metadata/ The timestamp of expiring by the next change	Mutable
LoadEndTS	Metadata/ The timestamp of expiring by the next load	Mutable
Hub keys	Hub keys of participating hubs in the relationship including the virtual hubs	All
Descriptives	Attributes measured/observed in the relationship	All

• A minimal subset of hub keys, optionally combined with LoadTS, forms the star composite primary key.

Sample Source Schema

Hub Star Target Model

Modeling Example
These ER diagrams represent a sample source schema and the target Hub Star model. Reference hubs are prefixed with ‘Ref’, and domain hubs are prefixed with ‘Dom’. The following table shows the entity mapping between the source and target models:

Source to Target Entity Mapping

Data Class	Soure Table	Hub	Star
Reference Data	City	RefCity	-
Reference Data	Country	RefCountry	-
Master Data	Customer	DomCustomer	StarCustomer
Master Data	Product	DomProduct	-
Transactional Data	Order	DomOrder	StarOrder
Transactional Data	OrderDetail	-	StarOrderItem

Hub Star Integration Matrix
The Hub Star Integration Matrix facilitates the incremental development of the target model. It shows the participation of hubs in stars at the intersections of rows and columns. For example, the following table represents the integration matrix for the previous example. (The sign × indicates that the hub key is also part of the star primary key):

Hub Star Integration Matrix

Star	DomCustomer	DomProduct	DomOrder	RefCity	RefCountry	Item	Time
StarCustomer	×			○			○
StarOrder	○		×				○
Example		○	×			×	○