You can specify relative column widths for a table to override the widths specified in your DITA document, or if no widths are specified in DITA. Otherwise, use one of the settings described in §33.4.8.1 Specifying a method for determining table column widths, such as:
[Tables] TableSizing = Percent
Suppose you have specified the following settings as defaults for all tables in your document:
[Tables] TableSizing = Adaptive Border = 1 Spacing = 0 Padding = 4
And suppose for one particular table format, TwoCol, you want relative column widths:
[TableSizing] TwoCol = Percent
This setting would make the width of each column in each TwoCol table a percent of the width of that particular table; but the setting would not specify the percentage.
If what you really want is for each TwoCol table to have columns of equal width, instead you would specify:
[TableCellAttributes] TwoCol = width="50%"
Naturally, this setting works only if all TwoCol tables have exactly two columns.
To set the width of the table itself, you could add:
[TableAttributes] TwoCol = width="100%"
This setting would eliminate your [Tables] settings for border, cellpadding, and cellspacing; so you would have to add them to the attribute list for TwoCol tables:
[TableAttributes] TwoCol = width="100%" border="1" cellpadding="4" cellspacing="0"