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Oracle® Data Mining User's Guide
12c Release 1 (12.1)

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3 Preparing the Data

This chapter explains how to create a table or view that can be used to build a model. This chapter contains the following topics:

Data Requirements

Data mining activities require data that is defined within a single table or view. The information for each record must be stored in a separate row. The data records are commonly called cases. Each case can optionally be identified by a unique case ID. The table or view itself can be referred to as a case table.

The CUSTOMERS table in the SH schema is an example of a table that could be used for mining. All the information for each customer is contained in a single row. The case ID is the CUST_ID column. The rows listed in Example 3-1 are selected from SH.CUSTOMERS.

Example 3-1 Sample Case Table

SQL> select cust_id, cust_gender, cust_year_of_birth, 
           cust_main_phone_number from sh.customers where cust_id < 11;

CUST_ID CUST_GENDER CUST_YEAR_OF_BIRTH CUST_MAIN_PHONE_NUMBER
------- ----------- ---- ------------- -------------------------
1        M               1946          127-379-8954
2        F               1957          680-327-1419
3        M               1939          115-509-3391
4        M               1934          577-104-2792
5        M               1969          563-667-7731
6        F               1925          682-732-7260
7        F               1986          648-272-6181
8        F               1964          234-693-8728
9        F               1936          697-702-2618
10       F               1947          601-207-4099

Note:

Oracle Data Mining requires single-record case data for all types of models except association models, which can be built on native transactional data. See "Using Market Basket Data".

Column Data Types

The columns of the case table hold the attributes that describe each case. In Example 3-1, the attributes are: CUST_GENDER, CUST_YEAR_OF_BIRTH, and CUST_MAIN_PHONE_NUMBER. The attributes are the predictors in a supervised model or the descriptors in an unsupervised model. The case ID, CUST_ID, can be viewed as a special attribute; it is not a predictor or a descriptor.

Oracle Data Mining supports standard Oracle data types as well as the following collection types:


DM_NESTED_CATEGORICALS
DM_NESTED_NUMERICALS
DM_NESTED_BINARY_DOUBLES
DM_NESTED_BINARY_FLOATS

See Also:

Data Sets for Classification and Regression

You need two case tables to build and validate classification and regression models. One set of rows is used for training the model, another set of rows is used for testing the model. It is often convenient to derive the build data and test data from the same data set. For example, you could randomly select 60% of the rows for training the model; the remaining 40% could be used for testing the model.

Models that implement other mining functions, such as attribute importance, clustering, association, or feature extraction, do not use separate test data.

Scoring Requirements

Most data mining models can be applied to separate data in a process known as scoring. Oracle Data Mining supports the scoring operation for classification, regression, anomaly detection, clustering, and feature extraction.

The scoring process matches column names in the scoring data with the names of the columns that were used to build the model. The scoring process does not require all the columns to be present in the scoring data. If the data types do not match, Oracle Data Mining attempts to perform type coercion. For example, if a column called PRODUCT_RATING is VARCHAR2 in the training data but NUMBER in the scoring data, Oracle Data Mining effectively applies a TO_CHAR() function to convert it.

The column in the test or scoring data must undergo the same transformations as the corresponding column in the build data. For example, if the AGE column in the build data was transformed from numbers to the values CHILD, ADULT, and SENIOR, then the AGE column in the scoring data must undergo the same transformation so that the model can properly evaluate it.

Note:

Oracle Data Mining can embed user-specified transformation instructions in the model and reapply them whenever the model is applied. When the transformation instructions are embedded in the model, you do not need to specify them for the test or scoring data sets.

Oracle Data Mining also supports Automatic Data Preparation (ADP). When ADP is enabled, the transformations required by the algorithm are performed automatically and embedded in the model along with any user-specified transformations.

Automatic and embedded data transformations are discussed in Chapter 4.

About Attributes

Attributes are the items of data that are used in data mining. In predictive models, attributes are the predictors that affect a given outcome. In descriptive models, attributes are the items of information being analyzed for natural groupings or associations. A table of employee data might contain attributes such as job title, date of hire, salary, age, gender, and so on.

Data Attributes and Model Attributes

Data attributes are columns in the data set used to build, test, or score a model. Model attributes are the data representations used internally by the model.

Data attributes and model attributes can be the same. For example a column called SIZE, with values S, M, and L, might be an attribute used by an algorithm to build a model. Internally, the model attribute SIZE would most likely be the same as the data attribute from which it was derived.

On the other hand, a nested column SALES_PROD, containing the sales figures for a group of products, would not correspond to a model attribute. The data attribute would be SALES_PROD, but each product with its corresponding sales figure (each row in the nested column) would be a model attribute.

Transformations also cause a discrepancy between data attributes and model attributes. For example, a transformation could apply a calculation to two data attributes and store the result in a new attribute. The new attribute would be a model attribute that has no corresponding data attribute. Other transformations such as binning, normalization, and outlier treatment, cause the model's representation of an attribute to be different from the data attribute in the case table.

See Also:

Target Attribute

The target of a supervised model is a special kind of attribute. The target column in the training data contains the historical values used to train the model. The target column in the test data contains the historical values to which the predictions are compared. The act of scoring produces a prediction for the target.

Clustering, feature extraction, association, and anomaly detection models do not use a target.

Nested columns and columns of unstructured data (such as BFILE, CLOB, or BLOB) cannot be used as targets. Target attributes must have a simple data type.

Table 3-1 Target Data Types

Mining Function Target Data Types

Classification

VARCHAR2, CHAR

NUMBER, FLOAT

BINARY_DOUBLE, BINARY_FLOAT

Regression

NUMBER, FLOAT

BINARY_DOUBLE, BINARY_FLOAT


You can query the *_MINING_MODEL_ATTRIBUTES view to find the target for a given model, as shown in Example 2-2 .

Numericals, Categoricals, and Unstructured Text

Model attributes are numerical, categorical, or unstructured (text). Data attributes, which are columns in a case table, have Oracle data types, as described in "Column Data Types".

Numerical attributes can theoretically have an infinite number of values. The values have an implicit order, and the differences between them are also ordered. Oracle Data Mining interprets NUMBER, FLOAT, BINARY_DOUBLE, BINARY_FLOAT, DM_NESTED_NUMERICALS, DM_NESTED_BINARY_DOUBLES, and DM_NESTED_BINARY_FLOATS as numerical.

Categorical attributes have values that identify a finite number of discrete categories or classes. There is no implicit order associated with the values. Some categoricals are binary: they have only two possible values, such as yes or no, or male or female. Other categoricals are multi-class: they have more than two values, such as small, medium, and large.

Oracle Data Mining interprets CHAR and VARCHAR2 as categorical by default, however these columns may also be identified as columns of unstructured data (text). Oracle Data Mining interprets columns of DM_NESTED_CATEGORICALS as categorical. Columns of CLOB, BLOB, and BFILE always contain unstructured data. For information about mining unstructured data, see Chapter 7.

The target of a classification model is categorical. (If the target of a classification model is numeric, it is interpreted as categorical.) The target of a regression model is numerical. The target of an attribute importance model is either categorical or numerical.

Model Signature

The model signature is the set of data attributes that are used to build a model. Some or all of the attributes in the signature should be present for scoring. The model accounts for any missing columns on a best-effort basis. If columns with the same names but different data types are present, the model attempts to convert the data type. If extra, unused columns are present, they are disregarded.

The model signature does not necessarily include all the columns in the build data. Algorithm-specific criteria may cause the model to ignore certain columns. Other columns may be eliminated by transformations. Only the data attributes actually used to build the model are included in the signature.

The target and case ID columns are not included in the signature.

Scoping of Model Attribute Name

The model attribute name consists of two parts: a column name, and a subcolumn name.

column_name[.subcolumn_name]

The column_name component is the name of the data attribute. It is present in all model attribute names. Nested attributes and text attributes also have a subcolumn_name component as shown in Example 3-2.

Example 3-2 Model Attributes Derived from a Nested Column

The nested column SALESPROD has three rows.

SALESPROD(ATTRIBUTE_NAME, VALUE)
--------------------------------
((PROD1, 300),
 (PROD2, 245),
 (PROD3, 679))

The name of the data attribute is SALESPROD. Its associated model attributes are:

SALESPROD.PROD1
SALESPROD.PROD2
SALESPROD.PROD3

Model Details

Model details reveal information about model attributes and their treatment by the algorithm. There is a separate GET_MODEL_DETAILS routine for each algorithm.

Transformation and reverse transformation expressions are associated with model attributes. Transformations are applied to the data attributes before the algorithmic processing that creates the model. Reverse transformations are applied to the model attributes after the model has been built, so that the model details are expressed in the form of the original data attributes, or as close to it as possible.

Reverse transformations support model transparency. They provide a view of the data that the algorithm is working with internally but in a format that is meaningful to a user.

Example 3-3 shows the definition of the GET_MODEL_DETAILS function for an Attribute Importance model.

Example 3-3 Model Details for an Attribute Importance Model

The syntax of the GET_MODEL_DETAILS function for Attribute Importance models is shown as follows.

DBMS_DATA_MINING.GET_MODEL_DETAILS_AI (
             model_name             VARCHAR2)
RETURN DM_RANKED_ATTRIBUTES PIPELINED;

The function returns DM_RANKED_ATTRIBUTES, a virtual table. The columns are the model details. There is one row for each model attribute in the specified model. The columns are described as follows.

attribute_name          VARCHAR2(4000)
attribute_subname       VARCHAR2(4000)
importance_value        NUMBER
rank                    NUMBER(38)

Using Nested Data

Oracle Data Mining requires a case table in single-record case format, with each record in a separate row. What if some or all of your data is in multi-record case format, with each record in several rows? What if you want one attribute to represent a series or collection of values, such as a student's test scores or the products purchased by a customer?

This kind of one-to-many relationship is usually implemented as a join between tables. For example, you might join your customer table to a sales table and thus associate a list of products purchased with each customer.

Oracle Data Mining supports dimensioned data through nested columns. To include dimensioned data in your case table, create a view and cast the joined data to one of the Data Mining nested table types. Each row in the nested column consists of an attribute name/value pair. Oracle Data Mining internally processes each nested row as a separate attribute.

Note:

O-Cluster is the only algorithm that does not support nested data.

Nested Object Types

Oracle Database supports user-defined data types that make it possible to model real-world entities as objects in the database. Collection types are object data types for modeling multi-valued attributes. Nested tables are collection types. Nested tables can be used anywhere that other data types can be used. You can learn more about collection types in Oracle Database Object-Relational Developer's Guide.

Oracle Data Mining supports the following nested object types:


DM_NESTED_BINARY_DOUBLES
DM_NESTED_BINARY_FLOATS
DM_NESTED_NUMERICALS
DM_NESTED_CATEGORICALS

Descriptions of the nested types are provided in Example 3-4.

Example 3-4 Oracle Data Mining Nested Data Types

describe dm_nested_binary_double
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              BINARY_DOUBLE

describe dm_nested_binary_doubles
 DM_NESTED_BINARY_DOUBLES TABLE OF SYS.DM_NESTED_BINARY_DOUBLE
 Name                                       Null?    Type
 ------------------------------------------ -------- ---------------------------
 ATTRIBUTE_NAME                                      VARCHAR2(4000)
 VALUE                                               BINARY_DOUBLE

describe dm_nested_binary_float
 Name                                      Null?    Type
 ----------------------------------------- -------- ---------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              BINARY_FLOAT
 
describe dm_nested_binary_floats
 DM_NESTED_BINARY_FLOATS TABLE OF SYS.DM_NESTED_BINARY_FLOAT
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              BINARY_FLOAT

describe dm_nested_numerical
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              NUMBER
 
describe dm_nested_numericals
 DM_NESTED_NUMERICALS TABLE OF SYS.DM_NESTED_NUMERICAL
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              NUMBER

describe dm_nested_categorical
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              VARCHAR2(4000)
 
describe dm_nested_categoricals
 DM_NESTED_CATEGORICALS TABLE OF SYS.DM_NESTED_CATEGORICAL
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ATTRIBUTE_NAME                                     VARCHAR2(4000)
 VALUE                                              VARCHAR2(4000)

Example: Transforming Transactional Data for Mining

Example 3-5 shows data from a view of a sales table. It includes sales for three of the many products sold in four regions. This data is not suitable for mining at the product level because sales for each case (product), is stored in several rows.

Example 3-5 Product Sales per Region in Multi-Record Case Format

PRODUCT   REGION         SALES
-------   --------   ----------
Prod1       NE           556432
Prod2       NE           670155
Prod3       NE             3111
.
.
Prod1       NW            90887
Prod2       NW           100999
Prod3       NW           750437
.
.
Prod1       SE            82153
Prod2       SE            57322
Prod3       SE            28938
.
.
Prod1       SW          3297551
Prod2       SW          4972019
Prod3       SW           884923
.
.

Example 3-6 shows how this data could be transformed for mining. The case ID column would be PRODUCT. SALES_PER_REGION, a nested column of type DM_NESTED_NUMERICALS, would be a data attribute. This table is suitable for mining at the product case level, because the information for each case is stored in a single row.

Example 3-6 Product Sales per Region in Single-Record Case Format

PRODUCT      SALES_PER_REGION
          (ATTRIBUTE_NAME, VALUE)
------    --------------------------
Prod1      ('NE' ,     556432)
           ('NW' ,      90887)
           ('SE' ,      82153)
           ('SW' ,    3297551)
Prod2      ('NE' ,     670155)
           ('NW' ,     100999)
           ('SE' ,      57322)
           ('SW' ,    4972019)
Prod3      ('NE' ,       3111)
           ('NW' ,     750437)
           ('SE' ,      28938)
           ('SW' ,     884923)
.
.

Oracle Data Mining treats each nested row as a separate model attribute, as shown in Example 3-7. (Note that the presentation in this example is conceptual only. The data is not actually pivoted before being processed.)

Example 3-7 Model Attributes Derived From SALES_PER_REGION

PRODUCT    SALES_PER_REGION.NE    SALES_PER_REGION.NW    SALES_PER_REGION.SE    SALES_PER_REGION.SW   
-------    ------------------    -------------------    ------------------    -------------------
Prod1                 556432                 90887                  82153                3297551
Prod2                 670155                100999                  57322                4972019
Prod3                   3111                 750437                 28938                 884923
.
.

Using Market Basket Data

Market basket data identifies the items sold in a set of baskets or transactions. Oracle Data Mining provides the association mining function for market basket analysis.

Association models use the Apriori algorithm to generate association rules that describe how items tend to be purchased in groups. For example, an association rule might assert that people who buy peanut butter are 80% likely to also buy jelly

Market basket data is usually transactional. In transactional data, a case is a transaction and the data for a transaction is stored in multiple rows. Oracle Data Mining association models can be built on transactional data or on single-record case data. The ODMS_ITEM_ID_COLUMN_NAME and ODMS_ITEM_VALUE_COLUMN_NAME settings specify whether the data for association rules is in transactional format.

Note:

Association models are the only type of model that can be built on native transactional data. For all other types of models, Oracle Data Mining requires that the data be presented in single-record case format

The Apriori algorithm assumes that the data is transactional and that it has many missing values. Apriori interprets all missing values as sparse data, and it has its own native mechanisms for handling sparse data.

See Also:

Oracle Database PL/SQL Packages and Types Reference for information on the ODMS_ITEM_ID_COLUMN_NAME and ODMS_ITEM_VALUE_COLUMN_NAME settings

Example: Creating a Nested Column for Market Basket Analysis

Association models can be built on native transactional data or on nested data. Example 3-8 shows how to define a nested column for market basket analysis.

Example 3-8 Convert to a Nested Column

The view SALES_TRANS_CUST provides a list of transaction IDs to identify each market basket and a list of the products in each basket.

describe sales_trans_cust
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- ----------------
 TRANS_ID                                              NOT NULL NUMBER
 PROD_NAME                                             NOT NULL VARCHAR2(50)
 QUANTITY                                                       NUMBER

The following SQL statement transforms this data to a column of type DM_NESTED_NUMERICALS in a view called SALES_TRANS_CUST_NESTED. This view can be used as a case table for mining.

CREATE VIEW sales_trans_cust_nested AS
             SELECT trans_id,
                     CAST(COLLECT(DM_NESTED_NUMERICAL(
                     prod_name, 1))
                     AS DM_NESTED_NUMERICALS) custprods
                  FROM sales_trans_cust
             GROUP BY trans_id;

This query returns two rows from the transformed data.

SELECT * FROM sales_trans_cust_nested 
               WHERE trans_id < 101000
               AND trans_id > 100997;
 
TRANS_ID  CUSTPRODS(ATTRIBUTE_NAME, VALUE)
-------  ------------------------------------------------
100998   DM_NESTED_NUMERICALS
          (DM_NESTED_NUMERICAL('O/S Documentation Set - English', 1)
100999   DM_NESTED_NUMERICALS
          (DM_NESTED_NUMERICAL('CD-RW, High Speed Pack of 5', 1),
           DM_NESTED_NUMERICAL('External 8X CD-ROM', 1), 
           DM_NESTED_NUMERICAL('SIMM- 16MB PCMCIAII card', 1))

Handling Missing Values

Oracle Data Mining distinguishes between sparse data and data that contains random missing values. The latter means that some attribute values are unknown. Sparse data, on the other hand, contains values that are assumed to be known, although they are not represented in the data.

A typical example of sparse data is market basket data. Out of hundreds or thousands of available items, only a few are present in an individual case (the basket or transaction). All the item values are known, but they are not all included in the basket. Present values may have a quantity, while the items that are not represented are sparse (with a known quantity of zero).

Oracle Data Mining interprets missing data as follows:

  • Missing at random — Missing values in columns with a simple data type (not nested) are assumed to be missing at random.

  • Sparse — Missing values in nested columns indicate sparsity.

Examples: Missing Values or Sparse Data?

The examples in this section illustrate how Oracle Data Mining identifies data as either sparse or missing at random.

Sparsity in a Sales Table

A sales table contains point-of-sale data for a group of products that are sold in several stores to different customers over a period of time. A particular customer buys only a few of the products. The products that the customer does not buy do not appear as rows in the sales table.

If you were to figure out the amount of money a customer has spent for each product, the unpurchased products would have an inferred amount of zero. The value is not random or unknown; it is zero, even though no row appears in the table.

Note that the sales data is dimensioned (by product, stores, customers, and time) and would often be represented as nested data for mining.

Since missing values in a nested column always indicate sparsity, you should ensure that this interpretation is appropriate for the data that you want to mine. For example, when trying to mine a multi-record case data set containing users' movie ratings of a large movie database, the missing ratings would be unknown (missing at random), but Oracle Data Mining would treat the data as sparse and infer a rating of zero for the missing value.

Missing Values in a Table of Customer Data

A table of customer data contains demographic data about customers. The case ID column is the customer ID. The attributes are age, education, profession, gender, house-hold size, and so on. Not all the data may be available for each customer. Any missing values are considered to be missing at random. For example, if the age of customer 1 and the profession of customer 2 are not present in the data, that information is simply unknown. It does not indicate sparsity.

Note that the customer data is not dimensioned. There is a one-to-one mapping between the case and each of its attributes. None of the attributes are nested.

Changing the Missing Value Treatment

If you want Oracle Data Mining to treat missing data as sparse instead of missing at random or missing at random instead of sparse, transform it before building the model.

If you want missing values to be treated as sparse, but Oracle Data Mining would interpret them as missing at random, you can use a SQL function like NVL to replace the nulls with a value such as "NA". Oracle Data Mining does not perform missing value treatment when there is a specified value. See Oracle Database SQL Language Reference for details about the NVL function.

If you want missing nested attributes to be treated as missing at random, you can transform the nested rows into physical attributes in separate columns — as long as the case table stays within the 1000 column limitation imposed by the Database. Fill in all of the possible attribute names, and specify them as null. Alternatively, you could insert rows in the nested column for all the items that are not present and assign a value such as the mean or mode to each one.