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 dipicts 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, dipict 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.