Information Technology Reference
In-Depth Information
4 . 3
P e r f o r m a n c e E v a l u a t i o n
4.3.1 Parameters
A simulator was developed to study the behavior of the aforementioned mapping
algorithms, based on a set of rich statistical parameters. The OO7 benchmark was
chosen to generate the access pattern graphs because of its rich schema graph for
a general object-oriented database application. The NASDAQ exchange
[50]
was
used as the base model, where data is in both textual and multimedia (graphics—
i.e., graphs and tables).
Table II
shows a brief description of the input and output
parameters. The simulator is designed to measure the average access delay for the
various input parameters.
Table III
provides a listing of the input parameters, along
with their default values and possible ranges. The default values are set as the value of
the parameter when other parameters are varied during the course of the simulation.
The ranges are used when the parameter itself is varied.
4.3.2 Results
4.3.2.1 Impact of Number of Objects.
Number of the objects on the
broadcast has effect on the broadcast length and consequently, affects the access
time—more nodes on the broadcast introduce additional distance between the ran-
domly requested objects.
Figure 14
shows the effect of varying the number of
requested objects on the average access delay. As expected in all three cases, the
average access delay increased as the total number of objects increased. Approxi-
mateLinearOrder and PartiallyLinearOrder schemes performed better than the con-
ventional children-depth first by taking linearity issue into consideration. Since the
T
ABLE
II
D
ESCRIPTION OF
P
ARAMETERS
Parameter
Description
Input parameters
Number of nodes
Number of objects within the graph (excluding replication)
Object size
Sizes of objects (small/medium/large)
Object-size distribution
Distribution of the sizes of objects within the database
Next-node ratio
Connectivity to next node (random or connection)
Out-degree distribution
Distribution of the type of nodes based on their out-degrees
Level distribution
Semantic connectivity of two objects (weak/normal/strong)
Percentage of popular objects
Percentage of objects requested more often than others
Replication frequency
The number of times a popular object is to be replicated
Output parameter
Average access delay
In a single query, the average delay between accessing two objects
