Wirtschaftsuniversität Wien Magisterarbeit - SemanticLab

webservers for administrative purposes as well as data to process customer orders, it
might have two statements. These data specific assertions are:
• A consequence should provide the users with information specifying why their data
is actually collected and why it may be valuable for a certain service, transaction
or feature. It is stated in a human-readable form using the CONSEQUENCE
element. This element is optional, its usage however is strongly recommended.
• If a websites does not collect identifiable data (so called non-identifiable data) or
if it anonymizes this data, it may set an indicator accordingly using the NON-
IDENTIFIABLE element. However, websites should note that the P3P specification
provides a strict definition of anonymized: ’In order to consider the data
”anonymized”, there must be no reasonable way for the entity or a third party to
attach the collected data to the identity of a natural person’ [W3Ca]. This element
is optional.
• How the data a website collects is going to be used has to be provided using the
PURPOSE element. The P3P vocabulary defines twelve purposes whereas the
twelfth provides a possibility to provide human-readable information. The other
eleven purposes have a predefined meaning. Table 3.1 recites the “Plain Language
Translations of P3P Vocabulary Elements” of the P3P specification for these twelve
elements according to [W3Ca].
• The RECIPIENT element states with which parties collected data will be shared.
P3P specifies six types of recipients which are listed in Table 3.2.
• The data-retention policy in effect must be defined using the RETENTION element.
Although no specific time is indicated, the five sub-elements can give users
an indication about the websites’ retention policy which can be supported by a
human-readable retention policy. Table 3.3 lists all sub-elements including their
meaning.
As with policy reference files, P3P policies can be assigned a language by using the
xml:lang attribute. This attribute is used to identify the language of human-readable
fields.
Another feature already highlighted is the policy lifetime. By setting the EXPIRE
element, website can provide information on how long a certain policy is valid, that is
when user-agents have to re-fetch a policy for a website or certain content elements.
Besides “normal” P3P policies, one can also define compact policies (CP) which
represent a summary of a websites’ P3P policy for a cookie. Compact policies are transmitted
via an additional HTTP response header CP. As the name suggests, compact
policies do not provide the same details as P3P policies. However, compact policies are
heavily used especially by Microsoft’s Internet Explorer which decides if a cookie is going
to be blocked or not solely based on compact policies [Cra02].
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