This section describes the predicates required for creating and destroying the access to external database tables.
ColumnName(Type [, ColumnOptions])
Type denotes the Prolog type to which the field should be converted and is one of:
integer | Convert to a Prolog integer. The input is treated as a decimal number. |
hexadecimal | Convert to a Prolog integer. The input is treated as a hex number. |
float | Convert to a Prolog floating point
number. The input is handled by the C-library function
strtod(). |
atom | Convert to a Prolog atom. |
string | Convert to a SWI-Prolog string object. |
code_list | Convert to a list of ASCII codes. |
ColumnOptions is a list of additional properties of the column. Supported values are:
sorted | The field is strictly sorted, but may have (adjacent) duplicate entries. If the field is textual, it should be sorted alphabetically, otherwise it should be sorted numerically. |
sorted(+Table) | The (textual) field is sorted using the ordering declared by the named ordering table. This option may be used to define reverse order,‘dictionary’order or other irregular alphabetical ordering. See new_order_table/2. |
unique | This column has distinct values for each row in the table. |
downcase | Map all uppercase in the field to lowercase before converting to a Prolog atom, string or code_list. |
map_space_to_underscore | Map spaces to underscores before converting to a Prolog atom, string or code_list. |
syntax | For numerical fields. If the field does not contain a valid number, matching the value fails. Reading the value returns the value as an atom. |
width(+Chars) | Field has fixed width of the specified number of characters. The column-separator is not considered for this column. |
arg(+Index) | For read_table_record/4, unify the field with the given argument of the record term. Further fields will be assigned index+1, ... . |
skip | Don't convert this field to Prolog. The field is simply skipped without checking for consistency. |
The Options argument is a list of global options for the table. Defined options are:
record_separator(+Code) | Character (ASCII) value of the character separating two records. Default is the newline (ASCII 10). |
field_separator(+Code) | Character (ASCII) value of the character separating two fields in a record. Default is the space (ASCII 32), which also has a special meaning. Two fields separated by a space may be separated by any non-empty sequence of spaces and tab (ASCII 9) characters. For all other separators, a single character separates the fields. |
encoding(+Encoding) | Text
encoding of the file. Values are iso_latin_1 (default),
utf8 or native. The latter uses the native
multibyte to unicode conversion. |
escape(+Code, +ListOfMap) | Sometimes,
a table defines escape sequences to make it possible to use the
separator-characters in text-fields. This options provides a simple way
to handle some standard cases. Code is the ASCII
code of the character that leads the escape sequence. The default is
-1, and thus never matched.
ListOfMap is a list of
From = To character mappings. The
default map table is the identity map, unless Code refers to
the
\ character, in which case
\b, \e, \n, \r and \t
have their usual meaning. |
functor(+Head) | Functor used by read_table_record/4.
Default is record using the maximal argument index of the
fields as arity. |
If the options are parsed successfully, Handle is unified with a term that may be used as a handle to the table for future operations on it. Note that new_table/4 does not access the file system, so its success only indicates the description could be parsed, not the presence, access or format of the file.