Database ODBC channel identifier returned from a call to RODM_open_dbms_connection
data_table_name
Database table/view containing the training dataset.
case_id_column_name
Row unique case identifier in data_table_name.
model_name
ODM Model name.
auto_data_prep
Whether or not ODM should invoke automatic data preparation for the build.
num_clusters
Setting that specifies the number of clusters for the clustering model.
max_buffer
Buffer size for O-Cluster. Default is 50,000.
sensitivity
A fraction that specifies the peak density required for separating a new
cluster. The fraction is related to the global uniform density. Default is 0.5.
retrieve_outputs_to_R
Flag controlling if the output results are moved to the R environment.
leave_model_in_dbms
Flag controlling if the model is deleted or left in RDBMS.
sql.log.file
File where to append the log of all the SQL calls made by this function.
Details
The O-Cluster algorithm creates a hierarchical grid-based clustering model, that is,
it creates axis-parallel (orthogonal) partitions in the input attribute space. The algorithm
operates recursively. The resulting hierarchical structure represents an irregular grid that
tessellates the attribute space into clusters. The resulting clusters define dense areas in the
attribute space.
The clusters are described by intervals along the attribute axes and the corresponding centroids
and histograms. A parameter called sensitivity defines a baseline density level. Only areas with
peak density above this baseline level can be identified as clusters.
The k-means algorithm tessellates the space even when natural clusters may not exist. For example,
if there is a region of uniform density, k-Means tessellates it into n clusters (where n is specified
by the user). O-Cluster separates areas of high density by placing cutting planes through areas of
low density. O-Cluster needs multi-modal histograms (peaks and valleys). If an area has projections
with uniform or monotonically changing density, O-Cluster does not partition it.
The clusters discovered by O-Cluster are used to generate a Bayesian probability model that is then
used during scoring (model apply) for assigning data points to clusters. The generated probability
model is a mixture model where the mixture components are represented by a product of independent
normal distributions for numerical attributes and multinomial distributions for categorical attributes.
Keep the following in mind if you choose to prepare the data for O-Cluster: 1. O-Cluster does not
necessarily use all the input data when it builds a model. It reads the data in batches (the default
batch size is 50000). It will only read another batch if it believes, based on statistical tests,
that there may still exist clusters that it has not yet uncovered. 2. Because O-Cluster may stop the
model build before it reads all of the data, it is highly recommended that the data be randomized.
3. Binary attributes should be declared as categorical. O-Cluster maps categorical data to numerical
values. 4. The use of Oracle Data Mining's equi-width binning transformation with automated estimation
of the required number of bins is highly recommended. 5. The presence of outliers can significantly
impact clustering algorithms. Use a clipping transformation before binning or normalizing. Outliers
with equi-width binning can prevent O-Cluster from detecting clusters. As a result, the whole
population appears to falls within a single cluster.
For more details on the algotithm implementation, parameters settings and
characteristics of the ODM function itself consult the following Oracle documents: ODM Concepts,
ODM Developer's Guide and Oracle SQL Packages: Data Mining, and Oracle Database SQL Language
Reference (Data Mining functions), listed in the references below.
Value
If retrieve_outputs_to_R is TRUE, returns a list with the following elements:
model.model_settings
Table of settings used to build the model.
model.model_attributes
Table of attributes used to build the model.
oc.clusters
General per-cluster information.
oc.split_predicate
Cluster split predicates.
oc.taxonomy
Parent-child cluster relationship.
oc.centroid
Per cluster-attribute centroid information.
oc.histogram
Per cluster-attribute hitogram information.
oc.rule
Cluster rules.
oc.leaf_cluster_count
Leaf clusters with support.
oc.assignment
Assignment of training data to clusters (with probability).
B.L. Milenova and M.M. Campos, Clustering Large Databases with Numeric and Nominal Values Using Orthogonal Projection, Proceeding of the 29th VLDB Conference, Berlin, Germany (2003).
Oracle9i O-Cluster: Scalable Clustering of Large High Dimensional Data Sets
http://www.oracle.com/technology/products/bi/odm/pdf/o_cluster_algorithm.pdf