<< >> Up Title

3.4 Use of Screens (Search Keys)


Principles of Screening

The CSD screen record contains bit-encoded summary information concerning a CSD entry. A setting of 1 indicates that a specific item of information is present in the entry (a `yes' setting), a setting of 0 indicates that it is absent (a `no' setting).

Many search queries posed to QUEST3D give rise to screen settings (some TEXT searches, 2D FRAGMENT SEARCHES, 3D GEOMETRIC SEARCHES). All of the screens set by the query TEST must be present in a given CSD entry before a detailed TEXT, FRAGMENT or GEOMETRIC search is undertaken. Thus, the screening process speeds the search by eliminating entries that cannot possibly be hits (usually over 95%) at a very early stage. Screens of this type are set and handled automatically by QUEST3D. They are listed in the full Documentation (Vol.3, Appendix 1).

User-Defined Screens

A further 155 screens are set in each CSD entry to record useful yes/no information about that entry. These screens can be accessed directly by the users of QUEST3D and are listed in Appendix D. Some of these screens are kept spare for further applications.

Setting SCREENs in QUEST3D

Searches Using SCREENs Alone

These searches can be very powerful and very fast

Thus: SCREEN 49 57 33 90 104

Locates:

Use of SCREENs with Search TESTs

SCREEN settings are commonly used as secondary search criteria in conjunction with primary search TEST(s). For example, we may wish to locate a specific chemical fragment (e.g. Examples 1 - 5) but restrict hits to entries that are:

Encode:

 SCREEN 34 -57 35 89 153


<< >> Up