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                                                 957
       SECTION 10.9                                                                Web Capture



       The E (expiration) entry specifies an expiration date for each source location
       associated with a content set. If the current date and time are later than those
       specified, the contents of the content set should be considered out of date with
       the original source.

       URL Alias Dictionaries

       When a URL is accessed via HTTP, a response header may be returned indicating
       that the requested data is at a different URL. This redirection process may be re-
       peated in turn at the new URL and can potentially continue indefinitely. It is not
       uncommon to find multiple URLs that all lead eventually to the same destination
       through one or more redirections. A URL alias dictionary represents such a set of
       URL chains leading to a common destination. Table 10.42 shows the contents of
       this type of dictionary.

                           TABLE 10.42 Entries in a URL alias dictionary
KEY   TYPE       VALUE

U     ASCII      (Required) The destination URL to which all of the chains specified by the C entry lead.
      string

C     array      (Optional) An array of one or more arrays of strings, each representing a chain of URLs
                 leading to the common destination specified by U.

       The C (chains) entry should be omitted if the URL alias dictionary contains only
       one URL. If C is present, its value is an array of arrays, each representing a chain
       of URLs leading to the common destination. Within each chain, the URLs are
       stored as ASCII strings in the order in which they occur in the redirection se-
       quence. The common destination (the last URL in a chain) may be omitted, since
       it is already identified by the U entry. (See implementation note 166 in Appendix
       H.)

       Command Dictionaries

       A Web Capture command dictionary represents a command executed by Web
       Capture to retrieve one or more pieces of source data that were used to create new
       pages or modify existing pages. The entries in this dictionary represent
       parameters that were originally specified interactively by the user who requested
       that the Web content be captured. This information is recorded so that the com-

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