Selection <selatt>

This syntax lets the user describe elements to include in, or exclude from, operations. Typically, the following criteria are used to define a selection:

• A class of elements or element types to be selected. Specify whether all members are to be included, or whether only items (the lowest level components in the hierarchy below a given element) should be included. See <selcla> below.

• A logical expression to be satisfied for all selected elements. These expressions return either True or False, and are usually used to check the values of attributes. Refer to PML 1 Expressions for further information.

• A physical volume in which all selected elements must lie or a physical volume which all selected elements must fully enclose. This volume is always orthogonal to the World coordinate axes. The user can specify this in terms of two diagonally opposite points of an enclosing box, or as a volume around an element (with an optional clearance around the element selected). See <selvol> below.

• A point in the hierarchy below which all selected elements must lie. Follow this with an exclusion list to exclude elements from the selection. See <selhie> below.

• A list (or collection), such as a drawlist, obstruction list or claimlist, of which the selected elements must be members.

All of these criteria are optional, except for class. If all element types are valid, this should be ALL.

If the user specifies more than one criterion, the specifications must be in the above order, as shown by the following graphs:

<selatt>= >-+- ALL -----------------------.

            |                             |

            |            .------<-----.   |

            |            |            |   |

            ‘- <selcla> -*- <selcla> -’   |

                         |                |

                         ‘----------------+--.

                                            |

  .-----------------<------------------------’

  |

  +- WIth --.

  |         |

  |- WHere -+- <expr> -.

  |                    |

  ‘--------------------+- <selvol> -.

                       |            |

                       ‘------------+- <selhie> -.

                                    |            |

                                    ‘------------+- <selfrom> -.

                                                 |             |

                                                 ‘-------------+-->

where <selcla> gives the class of items to be selected:

<selcla>=  >--+-- <noun> ---.

              |             |

              ‘--- <gid> ---+-- MEMbers --.

                            |             |

                            |-- ITEms ----|

                            |             |

                            ‘-------------+--->

<selvol>= >-+- EXACtly -.

            |           |

            '-----------+-EXCLusive WITHIN-.

                        |                  |

                        |- WITHIN ---------+- VOLume - <gid> -+- <expr>-.

                        |                  |                  |         |

                        |                  |                  '---------|

                        |                  |                            |

                        |                  '- <bpos> -+- TO - <bpos> ---|

                        |                             |                 |

                        |                             '--- <expr> ------|

                        |                                               |

                        '- ENCLosing -------+---- VOLume ----- <gid> ---|

                                            |                           |

                                            '- <bpos> -+- TO - <bpos> --|

                                                       |                |

                                                       '--- <expr> -----+>

<selhie> gives the point in the hierarchy below which elements are to be selected:

<selhie>=  >-- FOR -- <gid> --+-- <gid> ------------.

                              |                     |

                              ‘-- EXCLude - <gid> --+-->

<selfrom> limits the elements available to those in a specified list or collection:

<selfrom>=  >-- FROM --+-- !VAR -------.

                       |               |

                       |-- DRAWLIST ---|

                       |               |

                       |-- OBSTLIST ---|

                       |               |

                       ‘-- CLAIMLIST --+-->

The user can minimize the time taken for any selection operation by making the selection criteria as specific as possible, so that only relevant parts of the databases are searched for the required elements. Where known, specify the element type (for example, ALL BOX ...), the database element under which the search is to be restricted (for example,. ALL BOX FOR /ZONE1 ...), the volume in which the user is interested (for example,. ALL BOX WITHIN N5000 E5000 U0 TO N10000 E12000 U8000 ...), and so on. If the user does not do this, all databases in the current MDB will be searched, whether or not they contain relevant types of element, and performance will be impaired.