Databases Reference
In-Depth Information
For all three different user request scenarios presented in section 3, the
user access request evaluation is based on the overlaying procedure described
above. In [4], only the situation of MSR is considered, and the SMR type of
requests are supported in [5].
s
TPR-tree only supports authorizations of type
α
SM
and
α
MS
, and they are not able to support MMR. The support of MMR
is addressed in [7].
Static Requesters upon Mobile Resources (SMR)
: For a given user
request SMR, the procedure traverses the subtree under the root node
r
until
it reaches the leaf level. During this traversal, it compares the spatiotemporal
extent of a user request with that of each node
N
in the traversal path. One
would encounter three different cases:
•
enclosing:
If there exists any overlaid authorizations in
N
such that the
set of auth-subjects evaluated by
ge
contains the requester of SMR, then
all the moving objects that are located within the intersection area of
N
and
α
are returned.
•
overlapping:
If there exists any overlaid authorization in
N
such that the
set of auth-subjects evaluated by
se
contains the requester of SMR, only
the objects overlapping with
SMR
are returned. However, one still needs
to check authorizations overlaid on the descendants of
N
. This is because,
those overlaid on the descendents of
N
may include another spatiotemporal
region that
α
does not cover. If
N
is a leaf node, all the moving objects
that are overlapped with the intersection area of
N
and
α
and SMR
are returned.
•
disjoint:
The evaluation process is stopped because none of the moving
objects that are stored at the subtree rooted at
N
are within SMR
.
Moving Requesters upon Static Resources (MSR)
: The evaluation
starts by traversing the tree from the root node until it reaches the leaf level.
During the traversal, it checks if the spatiotemporal extent of each node in the
traversal path includes the current location of the requester of MSR. If so, all
the auth-objects contained in the spatiotemporal region covered by
ge
such
that the requester of MSR is in the set of subjects evaluated by
se
are col-
lected. If the requested resources are among this auth-objects set, the traversal
is stopped and a true is returned meaning that the requester is allowed to gain
access to the requested resource. Otherwise, traversal is continued. In case
N
is a leaf node, for each authorization
N
in
α
MS
, the auth-objects of
α
MS
are
included, if the intersection area of
N
and
α
encloses the location of the
requester.
Moving Requesters upon Moving Resources (MMR)
: Two traversals
of the tree can process MMR. The first traversal is to evaluate if the requester
is located in the authorized spatiotemporal region in order to access the mov-
ing resources. If this is true, another traversal can be performed to retrieve
the moving resources that authorize the requester to access their resources.
