Some Definitions

Term

Definition

Project Schema file

This file lists all the element types available in a project along with their attributes. All Table Schema files (see below) refer to a Project Schema file to map the columns in a table to element attributes.

In general, one Project Schema file can serve many Table Schema files.

Table Schema file

This file describes the tables used to retrieve data. Different table schemas may be appropriate for different reporting disciplines.

Table

A logical grouping of data.

A table consists of columns (attribute values) and table rows (element types).

When data is retrieved, the PDMS Provider searches for all elements of the types listed in the table rows and extracts the value of the attribute specified in the appropriate table row for each column.

Column

Each column in the table describes one element attribute whose value is to be returned when the table is queried. The column name is often the same as the attribute name, but does not have to be.

Table row

A table row describes what sort of data are to be returned. Each table row in a table specifies an element type and a list of bindings, one for each column.

A table contains one or more table rows.

In this document, "row" usually means "table row".

Data row

A row of data returned from the database corresponding to a single element. The values returned are determined by the entries in the table rows for that element type for the table.

Binding

A mapping in a table between the column and an attribute of an element. Each table row consists of an element type and a binding for each column of the table describing which attribute of the element supplies the data for that column.

Key column

A column in the table that uniquely identifies an object in the database.

A table must have a key column before any other column can be made writeable.

Practically, the key column must be either REFNO or NAME (REFNO is preferred). Key columns are always read-only.