My first Publication Agile-Data-Warehouse-Design-eBook | Page 308

BEAMāœ² Notation and Short Codes 289 Column Codes General Column Codes C ODE M EANING /U SAGE MD Mandatory. Column value should be present under normal conditions. Column is defined as nullable so it can handle errors. 2 NN Not Null. Column does not allow nulls. All SK and FK columns are not null by default. 5 ND NDn No Duplicates. Column must not contain duplicate values. The numbered version is used to define a combination of columns that must be unique. 9 Xn Exclusive. A dimensional attribute that is not valid for all members of a dimension. Used in conjunction with a DC defining characteristic. Number coded to identify mutually exclusive attributes or attribute groups and identify the defining characteristics it is paired with. Also used to denote exclusive facts that are only valid for certain dimensional values. 3, 8 DC DCn,n Defining Characteristic. Column value dictates which exclusive attributes or facts are valid. For example, Product Type DC defines which Product attributes are valid. Number coded when multiple defining characteristics exist in the same table. 3, 8 [W-type] Dimension type or name. The W (who, what, when, where, why, how) type of an event detail or the dimension name when a detail is a role; for example, Salesperson [Employee] where Salesperson is a role of the Employee dimension. Also used to show a recursive relationship within a detail table. 4, 6 {Source} Data source. The name of a column or field in a source system. Can be qualified with a table or filename if necessary (when different from the table default). 5 Unavailable Unavailable or incorrect. Column name or column code annotation denot- ing that source data is unavailable or does not comply with the current column type definition. For example, MD denotes that the source system does not treat the data as mandatory as it contains null or missing values. Gender denotes that Gender is not available. 5 [ dimension ] MD C HAPTERS Data Types C ODE M EANING /U SAGE C HAPTERS C Cn Character data type. The numbered version is used to define the maximum length. Overrides the default length. 5 N Nn.n Numeric data type. The numbered version is used to define precision. Overrides the default precision. 5 DT DTn Date/Time data type. The numbered version is used in duration formulas for derived facts; for example, Delivery Delay DF=DT2-DT1. Numbering can also denote default chronological order of milestones within an evolving event. 4, 5, 8