Virtual list view

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Virtual list view (VLV) is a GUI technique that can be employed where ordered lists with many entries need to be displayed. VLV provides a scrollable view of large sorted data set through a window with a few visible entries.

Note: IBM® Security Directory Server support for VLV follows the following Internet Drafts:
  • Virtual List View extension for LDAP search operations (draft-ietf-ldapext-ldapv3-vlv-09.txt).
  • Virtual List View extension for LDAP C API (draft-smith-ldap-c-api-ext-vlv-00.txt)
VLV search requests include criteria for identifying a wanted target entry and the number of entries before (before count) and number of entries after (after count) the target entry. The target entry is specified in the VLV request control by one of two methods:
  • Offset-based: This method provides target entry in VLV request control by indicating the target entry's offset within the list. The list here refers to ordered search result set. The server examines the content count (the client's estimate of the list count) and offset given by the client and computes the corresponding offset within the list, which is based on its own idea of content count.
    • An offset with value 1 and content count with value that is not equivalent to 1 indicate that the target is the first entry in the list.
    • If the values of offset and content count are equivalent, then, it indicates that the target is the last entry in the list.
    • A content count with value zero indicates that the server must use its own content count estimate.
  • Assertion-based: In this method, the client supplies an attribute assertion value. The assertion value is then compared against the values of the attribute that is specified as the primary sort key in the sort control that is attached to the search operation. The target entry is identified as the first entry in the list with value greater than or equal to the presented value.
    Note: It is possible that no entry satisfies the conditions that are specified in assertion-based method, in which case there is no target entry.

Consider an example where you need to display names in a telephone directory. Consider a telephone directory with the following 10 names in alphabetical order: Ari, Bob, Chris, David, John, Mike, Nancy, Peter, Rosy, and Ted.

Now, consider an offset-based VLV search request that specifies a sort on attribute cn with the following parameters: 
offset=4
before count=1
after count=1
content count=0 (This means that the server must use its own content count estimate)
The search in this case yields the following result: 
Chris, David, John
Now, consider an assertion-based VLV search request with the following parameters:
before count = 1 
after count = 1 
assertion = Jake
The search in this case yields the following result: 
David, John, Mike
Note: Since Jake is not present, the next entry in sorted order becomes the index entry, which in this case is John.

For information on how to enable VLV, see step 6 under Search settings.