EXAMPLE: Syntactic Medium in an Anchor State

Just what is an “Anchor State“? An example will explain this better.

Take an “extract-transform-load” (ETL) process in a Data Warehouse application that copies data from one system (a database) to another based on some criteria. In particular, the example organization needs to capture customer’s names for use in a business intelligence application measuring the success of marketing mass-mailings. An ETL process will be defined (in terms used within the Metamorphic Modeling convention) as a transformation from a source Anchor State (source) to a target Anchor State(target). The syntactic medium of the source application contains a table called “EMPLOYEE”. This data structure has been co-opted by the user organization to include customer information. The organization has chosen to use this table to represent customers since it is the only data structure available in their system that associates a person’s name to an address, telephone number and e-mail account, and it has no other means of recording this information about its customers.

 The source Anchor State has been constrained, therefore, to the “EMPLOYEE” data structure, and to the set of symbols within that medium which represent customers. That same medium, in a different Anchor State, may have been constrained to the set of “managers”.

 So, how does the ETL process recognize the set of symbols within the “EMPLOYEE” data structure that represent customers? The user organization realized that the application containing this data structure also contained a table called “EMPLOYEETYPE” which contains user-defined codes for defining types of employees. This table’s primary key is a coded value stored in a field named “EMPTYPE”, which also appears as a foreign key reference in the “EMPLOYEE” table. The organization decided to create a symbol, namely a code in this EMPLOYEETYPE table to represent the “customer type”. Then, whenever they want to record information about a customer in the EMPLOYEE table, they assign this code value to the “EMPTYPE” column on the row representing this customer.

 The following figure depicts a portion of an “Entity Relation Diagram” which defines the “EMPLOYEE” and “EMPLOYEETYPE” tables in this application. It also shows a subset of the values contained within the “EMPLOYEETYPE” table, as defined by this organization.

Example Employee Table Data Model

Example Employee Table Data Model

As can be seen in the figure, there are actually three different “EMPLOYEETYPE” codes defined to represent the concept of “customer”. These are EMP_TYPE values 5, 6, and 7, representing “Customers”, “Premier Customers” (which the organization has defined as important customers), and “Good Customers”. Asside from the “business practice” that these three types can be used to differentiate “customers” from other types of entities, there is nothing intrinsic to the structures that indicates this. Hence, from an application standpoint, all types are equal and will be manipulated in the same way.

 From the point of view of the ETL under development, however, the significance of the usage of these three codes is critical to its proper operation. The source Anchor State for the ETL is defined as the set of raw symbols within the “EMPLOYEE” table that have one of the “customer” type code values in their corresponding EMPTYPE column. For this ETL (transformation), the EMPTYPE column and its values represent the semantic marker for “customer” in this source Anchor State. The Anchor State therefore consists of the data structures, “EMPLOYEE” and “EMPLOYEETYPE”, and the constraint that only the rows of the “EMPLOYEE” table where the EMP_TYPE value is 5, 6, or 7 define what the ETL should consider to be “customers”.

 

All pages are Copyright (C) 2004, 2009 by Geoffrey A. Howe
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