The Star_Base conditional request

Spadaccini, N.; Hall, S. R.; McMahon, B.

doi:10.1107/97809553602060000752

International
Tables for
Crystallography
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

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International Tables for Crystallography (2006). Vol. G. ch. 5.2, p. 492

Section 5.2.3.3. The Star_Base conditional request

N. Spadaccini,^a ^* S. R. Hall^b and B. McMahon^c

^a School of Computer Science and Software Engineering, University of Western Australia, 35 Stirling Highway, Crawley, Perth, WA 6009, Australia,^bSchool of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Perth, WA 6009, Australia, and ^cInternational Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England
Correspondence e-mail: nick@csse.uwa.edu.au

5.2.3.3. The Star_Base conditional request

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While a data request allows retrieval of data items according to name, conditional requests allow retrieval of data items by value. The general form of a conditional request may be characterized as <data request><operator><text string>, where <data request> is any data request as defined in the preceding section, <operator> is any of the test operators defined below, and <text string> is a string pattern against which values of data items retrieved by the data request are matched according to the operator specified.

Conditional requests may be combined by set operators &, | and ! to provide logical AND, OR and NOT tests. Table 5.2.3.1 lists the allowed constructions for a conditional request. A bare data request is considered a degenerate case of a conditional request.

Table 5.2.3.1 | top | pdf |
Permitted constructions for a Star_Base conditional request

!<conditional request>

The construction <conditional request> & <conditional request> allows for the conjunction of conditionals. All data are returned (including context) from the intersection of sets of data that individually satisfy the conditions to be a non-empty set.

It is important to note that the conjunction of conditionals based on different data names is the empty set.

The construction <conditional request> | <conditional request> allows for the disjunction of conditionals. All data are returned (including context) from the union of sets of data that individually satisfy the conditions to be a non-empty set.

The construction !<conditional request> allows for the negation or complement of conditionals. All data are returned (including context) from the universal set of data that do not satisfy the conditions of the conditional request. The universal set is defined as the input file.

Table 5.2.3.2 lists the permitted value-matching operators when a retrieved data value is compared with a target text string in the basic test <data request><operator><text string> described above. (If the <text string> contains white-space characters, it must be quoted with matching single or double quotes. The test is performed on the value of the text string, i.e. the complete text string including white-space characters but omitting the surrounding quote characters.)

Table 5.2.3.2 | top | pdf |
Value-matching operators in Star_Base conditional requests

Requests are of the form <data request> <operator> <text string>. The second column describes the relationship that data identified by the <data request> must satisfy against the <text string> in order to be returned as part of the result set.

Operator	Relationship
Text comparison operators:
$[\sim=]$	Is identically equal to
?=	Includes as a substring
$[\sim\lt]$	Is less than (in ASCII order)
$[\sim\gt]$	Is greater than (in ASCII order)
$[\sim!=]$	Is not identically equal to
?!=	Does not include as a substring
$[\sim\lt=]$	Is not greater than (in ASCII order)
$[\sim\gt=]$	Is not less than (in ASCII order)

Numerical comparison operators:
=	Is equal to
<	Is less than
>	Is greater than
!=	Is not equal to
<=	Is not greater than
>=	Is not less than

Two classes of operators are defined. Text operators may be used to test for string equality, substring containment or greater and lesser values (where the `greater' and `lesser' values for text strings are based on the ASCII character set ordering sequence). These tests are valid for any STAR application. Numerical operators permit comparison of the numerical values implied by the returned data-value strings. Recall from Chapter 2.1 that data values in STAR are specified only as character strings. Casting to different types may be performed by specific applications, but is not defined for arbitrary STAR applications. Nevertheless, Star_Base recognizes that a majority of STAR applications will in fact specify numeric types, and therefore allows for numerical comparisons based on interpretations of certain value strings according to the conventions adopted by CIF for the numb data type (Section 2.2.7.4.7.1 ). Such values may be given as integers, real numbers or in scientific notation.

References

International Tables for Crystallography (2006). Vol. G. ch. 5.2, p. 492