Key Concepts
Pentaho Metadata Editor (PME) is a tool that builds Pentaho metadata domains and models. A Pentaho metadata model maps the physical structure of your database into a logical business model. These mappings are stored in a centralized metadata repository and allow administrators to:
create business-language definitions for complex database tables
decrease the cost and impact associated with low level database changes
set security parameters limiting user's report access to data
drive formatting on text, date and numeric data improving report maintenance
localize the information depending on the user's regional settings
The domain encapsulates all of the business objects created, stored and used in the metadata layer. A domain may consist of one or more connections, one or more models, security information, business tables, business views, categories, columns and concepts.
The Physical Layer of a Pentaho domain encompasses connections, physical tables and physical columns. These objects represent the database(s) you are trying to model and enrich with metadata. The Physical Layer is not considered part of the business model, because not all connections defined in the Physical Layer will be used in every business model.
Today, multiple business models can be created in one domain, but those models must have one and only one connection reference. This means that you cannot mix and match physical tables from two different connections in the same model.
This prevents the model from supporting multiple data sources, as well as severely limits the Pentaho Metadata Editor's ability to allow table changes across connections, a feature necessary for moving from dev to production databases, for example. Fortunately, you can get around the latter with a bit of hand-editing XML.
The Abstract Business Layer is the heavy lifter in the metadata business model. The business model encompasses the Abstract Business Layer and the Business View.
In the Abstract Business Layer, you have business tables, business columns, and business relationships.
You can create business tables for any physical table you have defined in the Physical Layer. You can also create more than one business table to reference the same physical table. The same rules apply for business columns. This can be useful in a multitude of scenarios, filtering security or even data at this level being one example.
The business table keeps a reference to the physical table that it models, and this allows a metadata inheritance relationship between physical tables and business tables. If you define metadata on a physical table, the business table will inherit that metadata, unless and until the business table itself has overridden the inherited metadata. This concept operates on a metadata property to property basis, meaning that each property can be overridden individually.
The same relationship exists between physical columns and business columns. If you define metadata on a physical column, the business column will inherit that metadata, unless and until the business column itself has overridden the inherited metadata.
Then there are relationships. These relationships are mappings that you define to describe the relational (or other) bonds between your business tables. One example may be a one to many relationship, between a customer table and an orders table.
The strength in metadata relationships is that you can identify relationships between columns or tables in the Abstract Business Layer that may not be obvious in the Physical Layer. An example would be to compare budget, actual and sales numbers, using a formula-derived business column that is specific to your business rules.
The Business View is the part of the business model that applications will operate against, and end-users will see. The Business View is nothing more than "buckets" (called categories) for you to re-arrange and re-organize your business columns in a fashion that makes sense to the consumers of the data.
In the Business View, you can create any number of categories and arrange your business columns in those categories however it best suits your business, mixing and matching columns that derived from different business tables, even adding business columns more than once to different categories. The only restriction to the Business View is you cannot add the same business column more than once to a single category.
You can define table or column level security to metadata used by the Pentaho BA server. Before you can enforce security, you must define settings that allow the Metadata Editor to communicate with the BA server. The Metadata Editor must be able to retrieve the lists of users, roles and access control lists (ACLs) needed.
You can also define row-level security which allows you to control the results that are returned in a query based on a user's security level. You can specify which rows of data each User Role or User ID can retrieve from the database, based on some column of data, or combination of columns of data.
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