NASIS Metadata Overview

Database Structure Guide Narrative Document

This document discusses the physical design conventions used in the implementation of a NASIS database. It discusses categories of tables, naming conventions, custom data types and how objects are identified. It includes an extensive discussion about how class (coded) attributes are handled in a NASIS database. It also details exactly how referential integrity is implemented in a NASIS database.

Attribute Report

The Attribute Report lists all attributes in a NASIS database, independent of the table or tables in which those attributes occur. The characteristics of an attribute in this report are characteristics that are consistent for an attribute, regardless of the table in which an attribute occurs. This is the only report that provides attribute definitions.

Another important feature of this report is that it provides the name of the choice list (domain) associated with an attribute, for attributes whose values are restricted to a finite set of fixed choices. This choice list name, and the choices associated with this domain, can be found in the Choice List Report.

The Attribute Report is generated from the MS Access NASIS Repository.

Choice List Report

The Choice List Reports displays all of the static domains in a NASIS database. A particular choice list may be associated with more than one attribute. An attribute may be associated with one and only one choice list.

In this report, the column labeled “Obsolete?” indicates whether a particular choice is currently considered valid. A NASIS database may have older records with attributes with choice values that were once valid but are now considered obsolete.

The Choice List Report is generated from the MS Access NASIS Repository.

Table Structure Report

The Table Structure report shows the columns that make up a table in a NASIS database, and some of the attributes of those columns. This is the only report that provides table definitions.

The column labeled “Sequence” records the default left to right display sequence of columns in the NASIS editor. It does not necessarily represent the physical order of the columns in a table. Relational database theory states that the order of the columns in a table should be immaterial.

The column labeled “Exp. Var.” denotes how the variability of an attribute as measured in the real world, is expressed. A column where “Exp. Var.” is “H, L, RV” is actually implemented as three columns in a physical NASIS database. “L” corresponds to the low end of the expected range. “H” corresponds to the high end of the expected range. “RV” corresponds to the expected or “representative” value.

The column labeled “Calc?” indicates if a calculation procedure is available to generate the value of an attribute. An attribute where “Calc?” is “Yes” is actually implemented as two columns in a physical NASIS database. One column contains the actual value of the attribute. A corresponding status column indicates if that value was manually entered (“M”) or was generated by the calculation procedure (“C”). A calculation status column may be null when no data has ever been entered for a column, or when a calculation procedure was added after a column was originally populated.

The Table Structure Report is generated from the MS Access NASIS Repository.

Table Index Report

The Index Report shows what indexes are defined for tables in a NASIS database. This report includes both duplicate and unique indexes. The reason for this report is that one cannot understand or effectively query a database without knowing what unique constraints are defined.

The Table Index Report is generated from the MS Access NASIS Repository.

Relationship Report

The Relationship Report shows on what columns two related tables in a NASIS database are joined. It indicates what table corresponds to the parent and what table corresponds to the child. The Relationship Report shows the cardinality of the relationship, whether the relationship is mandatory or optional and the delete rule for the relationship (restrict (fail) or cascade). Like the Index Report, the reason for this report is that one cannot understand or effectively query a database without knowing exactly how tables are related.

The Relationship Report is generated from the MS Access NASIS Repository.

Link Report

The Link Report shows what columns are displayed in the NASIS editor, in place of the surrogate foreign keys (system generated meaningless numbers) employed in a NASIS database. The Link Report is not necessary to understand or effectively query a NASIS database. The Link Report merely helps in understanding why not all of the columns seen in the Table Structure Report are visible in the NASIS editor. This report details exactly what columns from the related or lookup table are displayed in place of a surrogate foreign key.

The Link Report is generated from the MS Access NASIS Repository.

Traditional Data Structure Diagrams

This is the traditional multi-colored data structure diagram that we have provided since version 1.0 of NASIS. It depicts the parent-child relationships between tables in a NASIS database or distribution format using lines with arrows on one end. The end without the arrow is attached to the parent, and the end with the arrow is attached to the child.

Traditional data structure diagrams that correspond to a version of a NASIS database, as opposed to a version of a distribution format, depict three possible types of relationships. A solid relationship line denotes an edit relationship between two tables. This means that the two tables are displayed and edited in the same NASIS window. This also means that it is possible to navigate between these two tables using the NASIS editor Up Table and Down Table functions.

A heavy solid relationship line denotes a default down table edit relationship between two tables. This means that if the cursor is in a row of the parent table, and the user has not yet visited any of the child tables of that parent, when the user selects the Down Table function in the NASIS editor, the child table involved in the relationship will be displayed by default.

A dashed relationship line denotes a load related/find related relationship between the two tables. This means that the two tables are not displayed and edited in the same NASIS window, but that the NASIS editor Load Related and Find Related functions may be used to navigate between the two tables involved in the relationship.

Traditional Data Structure Diagrams were created with Visio 5.0 Professional.

Technical Data Model Diagrams

This document contains entity relationship diagrams and physical data models. These diagrams provide a graphical representation of the relationships between conceptual (business oriented) entities in an entity relationship diagram and between physical tables in a physical data model. This document contains a primer on the symbology used in such diagrams.

This document was not available prior to version 4.0 of NASIS.

Metadata Change Report

This report is actually a concatenated set of reports showing the metadata changes between two versions of the same information system. This report includes the following categories: Tables Added, Tables Dropped, Table Changes, Columns Added, Columns Dropped, Column Changes, Indexes Added, Indexes Dropped, Index Changes, Relationships Added, Relationship Dropped, Relationship Changes, Domains Added, Domains Dropped, Domain Changes, Choices Added, Choices Dropped and Choice Changes.

If some entity has been added, its subentities will not be categorized as “added”. For example, if a new table is added, that table’s columns will not be included in the Columns Added report. If a new domain is added, that domain’s choices will not be included in the Choices Added report.

MS Access Template Database

An MS Access template database is an empty MS Access database that contains the tables, indexes and relationships that correspond to an export format that NASIS is capable of producing. Typically such a template database also includes functions for importing data from a set of ASCII delimited text files, as well as a variety of reports.