Birkdale Computing

ross-mapping[i] business data elements (BDEs) from requirements or business glossaries all the way through to the physical data structures that store these data elements can be tricky.  This process is made easier if a logical data model (LDM) is implemented between the business side and the technology model upon which the physical implementation is based.

In this article I will show two styles of cross-mapping between the BDEs of the business glossary and the data storage structures defined in the physical data model (PDM).  The two styles are called “Column Style” mapping and “Cell Style” mapping.

Column Style can apply to the cross-mapping of BDEs with both base tables[ii] and reference tables.  Cell Style mapping takes Column Style a step further for reference data and maps the individual values of a reference BDE to individual cells, or row column coordinates, in the database.  If each reference value needs to be implemented in the technology separately a Cell Style mapping is needed.

Also some BDEs are atomic in that there is no inherent structure in the business data element.  I call these Simple BDEs.  Some BDEs have an inherent structure which depends on the scope of their business definition.  These structures are often in the form of a container and its contents.  I call these Compound BDEs.

Some examples of each style follow.  Figure 1 shows an example of a Column Style mapping of a Simple BDE[iii] to a single Column of a single base Table in the database.  Using the terms “Table” and “Column” gives the impression that these mapping styles apply only to relational databases.  This is not true.  The concepts here can apply to “NoSQL” databases as well, such as Key-Value Stores, Column Family Databases and Document Databases.  These types of databases have been referred to as Aggregate-Oriented Databases.[iv]

Figure 1.

Figure 2 shows a Column Style mapping of a Simple BDE to a single Column of a single reference Table in the database.  Note here that because it is a reference data mapping that the valid values of the reference BDE do not get specifically mapped to any structure or data in the database.  In this case the valid reference values may be defined and maintained in the business glossary in an appropriate manner but there is no explicit mapping link between them and any thing in the data model or database.  Also note that I am not saying that the reference values are not in the database.  They almost certainly are, since the applications would presumably not function properly if they were not.  But the values themselves (“Unknown”, “IFRS”, US GAAP”, etc.) are not considered BDEs.

Figure 2.

Figure 3 is a Column Style mapping of a Compound BDE to multiple Columns of a base Table in the database.  Note here that the BDE maps to two Columns in the same Table.  It could, of course, map to only one Column, or to many more Columns in many more Tables.  The point of this example is not how may times the BDE maps to various Columns but that it is a Compound BDE.  “Current Assets.Cash”[v] really identifies two business concepts, “Current Assets” which is a section of a financial statement, and “Cash” which is the most liquid kind of asset.  In terms of a financial statement, cash is a type of current asset.  For whatever reason, probably because cash itself can occur in multiple contexts, the business found it necessary to identify the financial statement use of cash in its own BDE.  Cash could also, for example, be a type of transaction, which would be another BDE.

Figure 3.

In Figure 4 we have an example of Cell Style mapping.  Here, the same Compound BDE that was used in Figure 3, “Current Cash.Assets” is broken apart into its two separate parts, and each is mapped with a different Column in a different reference Table in the database.  Both of these tables are reference Tables.  One contains the name of the types of financial statement templates used by the system (financial_statement_templates) to which “Current Assets” is mapped.  The other contains the names of the types of lines on those financial statements (financial_statement_line_templates) to which “Cash” is mapped.  It is unlikely that “Current Assets” would be mapped to multiple database Columns, but because of the multiple meanings of “Cash” there could be multiple mappings between it and multiple database Columns.

Figure 4.

Note that Cell Style mapping requires mapping to the data content of the database and not just its structure, or metadata.  This needs to be taken on with great caution and requires a consensus for how the words (e.g. “Cash”) used in the glossary are conveyed to and used in the Transaction Activity Data[vi] of the database to determine the actions of any application accessing the data.  Cash is simple, but any time you rely on reading a string to determine a code path you create an external dependency in the code.  However, if the business changes the name of a Cell Style mapped BDE there should be a documented path to where and how that value is used by any application that accesses it in the database.  This fact alone makes any system more maintainable and sustainable.

[i] The word “cross-mapping” is used to imply that the mapping goes both ways, from business to technology, and from technology to business.  This allows the documentation of the system to more accurately describe the entire enterprise architecture by creating valid and traceable links back and forth between the business architecture and the technical architecture.  By creating an interface between the two aspects of the enterprise architecture, business people can more confidently make decisions based on the data they see, knowing with confidence it is reliably stored and processed, and technical people can more confidently know the data they collect, manipulate and provide does in fact represent what business side intends for it to be.

[ii] I use the term “base table” here to refer to the realization of the bottom four of the six layers of data described by Malcolm Chisholm in his article “What is Master Data” originally published February 6, 2008.  http://www.b-eye-network.com/view/6758 .  These include Enterprise Structure Data, Transaction Structure Data, Transaction Activity Data and Transaction Audit Data.

[iii] The numbers (128, 600 and 1) that follow the name of each BDE in the examples are purely arbitrary and are there only to indicate that BDE’s should be numbered in the catalog for indexing purposes.

[iv] See Pramod J. Saladage and Martin Fowler, NOSQL Distilled, A Brief Guide to the Emerging World of Polyglot Persistence, Addison-Wesley, 2013.

[v] Note the “.” Between Current Assets and Cash.  This is just to make it easier the tell that the BDE is compound.  Don’t count on always having a separator between the parts of a Compound BDE.  The glossary tool may simply not support it or the in-depth analysis to identify the two parts may not have been made.  As a data modeler you may have to do this analysis yourself.

[vi] Please refer to note ii above.