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Oracle® Warehouse Builder Concepts
11g Release 2 (11.2)

Part Number E10581-02
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8 Data Quality Management

This section discusses data quality management and data profiling. Through data management capabilities, OWB ensures consistent, dependable data quality. Data profiling is the first step for any organization to improve information quality and provide better decisions.

This section contains these topics:

About Data Quality Management Processes and Phases

OWB offers a set of features that assist you in creating data systems that provide high quality information to your business users. With OWB you can implement a process that assesses, designs, transforms, and monitors data quality. The aim of building a data warehouse is to have an integrated, single source of data that can be used to make business decisions. Since the data is usually sourced from a number of disparate systems, it is important to ensure that the data is standardized and cleansed before loading into the data warehouse.

Using OWB for data management provides the following benefits:

The rest of this section is devoted to discussing the phases of implementing and using data quality processes.

Phases in the Data Quality Lifecycle

Ensuring data quality involves the following phases:

Figure 8-1 shows the phases involved in providing high quality information to your business users.

Figure 8-1 Phases Involved in Providing Quality Information

Description of Figure 8-1 follows
Description of "Figure 8-1 Phases Involved in Providing Quality Information"

Quality Assessment

In the quality assessment phase, you determine the quality of the source data. The first step in this phase is to import the source data, which could be stored in different sources, into OWB. You can import metadata and data from both Oracle and non-Oracle sources.

After you load the source data, you use data profiling to assess its quality. Data profiling is the process of uncovering data anomalies, inconsistencies, and redundancies by analyzing the content, structure, and relationships within the data. The analysis and data discovery techniques form the basis for data monitoring. For a quick summary of data profiling, see "Data Profiling: Assessing Data Quality".

Quality Design

The quality design phase consists of designing your quality processes. You can specify the legal data within a data object or legal relationships between data objects using data rules. For more information about data rules, see "Data Rules: Enforcing Data Quality".

Quality Transformation

As part of the quality design phase, you also design the transformations that ensure data quality. These transformations could be mappings that are generated by OWB as a result of data profiling or mappings you create. The quality transformation phase consists of running the correction mappings you designed to correct the source data.

Quality Monitoring

Data monitoring is the process of examining warehouse data over time and alerting you when the data violates business rules set for the data. For more information about data monitoring, see "Data Auditors: Monitoring Data Quality".

Data Profiling: Assessing Data Quality

Data profiling enables you to assess the quality of your source data before you use it in data integration scenarios and systems. OWB provides the Data Profile Wizard to guide you through creating a data profile, and the Data Profile Editor to configure and manage data profiles. Because data profiling is integrated with the ETL features in OWB and other data quality features, such as data rules and built-in cleansing algorithms, you can also generate data cleansing mappings and schema correction scripts. This enables you to automatically correct any inconsistencies, redundancies, and inaccuracies in both the data and metadata.

Data profiling enables you to discover many important things about your data. Some common findings include:

To begin the process of data profiling, you first use the Data Profile Wizard to create a data profile from within the Design Center. You then use the Data Profile Editor to run data profiling on the objects contained in the data profile, and to create correction tables and mappings.

Data Rules: Enforcing Data Quality

A data rule is a definition of valid data values and relationships, which determine legal data within a table or legal relationships between tables. Data rules can be applied to tables, views, dimensions, cubes, materialized views, and external tables. They are used in many situations including data profiling, data and schema cleansing, and data auditing.

The metadata for a data rule is stored in the workspace. To use a data rule, you apply the data rule to a data object. For example, you could create a data rule called gender_rule, which could specify that valid values are 'M' and 'F'. You could then apply this data rule to the emp_gender column of the Employees table. Applying the data rule ensures that the values stored for the emp_gender column are either 'M' or 'F'. You can view the details of the data rule bindings on the Data Rule tab of the Data Object Editor for the Employees table.

A data rule can be derived from the results of data profiling, or it can be created using the Data Rule Wizard or OMB*Plus scripting commands.

See Also:

These topics in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide:

Data Auditors: Monitoring Data Quality

OWB provides a way to create custom data auditors, which are processes that provide data monitoring by validating data against a set of data rules to determine which records comply and which do not. Data auditors gather statistical metrics on how well the data in a system complies with a rule by auditing and marking how many errors are occurring against the audited data. The monitoring process builds on your data profiling and data quality initiatives.

OWB Data Profiling Features

Using the data profiling features in OWB enables you to:

See Also:

"Performing Data Profiling" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide for detailed information and procedures

Types of Data Profiling

The selection of data objects determines which aspects of that data that you can profile and analyze.

Data profiling offers these main types of analysis:

Figure 8-2 displays a representation of the types of data profiling and how you can perform each type.

Figure 8-2 Data Profiling Overview

Description of Figure 8-2 follows
Description of "Figure 8-2 Data Profiling Overview"

Attribute Analysis

Attribute analysis seeks to discover both general and detailed information about the structure and content of data stored within a given column or attribute.

Attribute analysis consists of:

Pattern Analysis 

Pattern analysis attempts to discover patterns and common types of records by analyzing the string of data stored in the attribute. It generates several regular expressions that match many of the values in the attribute, and reports the percentages of the data that comply with each candidate regular expression. OWB can also search for data that conforms to common regular expressions, such as dates, e-mail addresses, telephone numbers and Social Security numbers.

Table 8-1 shows a sample attribute, Job Code, that could be used for pattern analysis.

Table 8-1 Sample Columns Used for Pattern Analysis

Job ID Job Code

7

337-A-55

9

740-B-74

10

732-C-04

20

43-D-4


Table 8-2 shows the possible results from pattern analysis, where D represents a digit and X represents a character. After looking at the results and knowing that it is company policy for all job codes be in the format of 999-A-99, you can derive a data rule that requires all values in this attribute to conform to this pattern.

Table 8-2 Pattern Analysis Results

Job Code % Occurred

999-A-999

75%

99-A-9

25%


Domain Analysis 

Domain analysis identifies a domain or set of commonly used values within the attribute by capturing the most frequently occurring values. For example, the Status column in the Customers table is profiled and the results reveal that 90% of the values are among the following values: "MARRIED", "SINGLE", "DIVORCED". Further analysis and drilling down into the data reveal that the other 10% contains misspelled versions of these words with few exceptions. Configuration of the profiling determines when something is qualified as a domain; therefore, be sure to review the configuration before accepting domain values. You can then let OWB derive a rule that requires the data stored in this attribute to be one of the three values that were qualified as a domain.

Data Type Analysis 

Data type analysis enables you to discover information about the data types found in the attribute. This type of analysis reveals metrics such as minimum and maximum character length values as well as scale and precision ranges. In some cases, the database column is of data type VARCHAR2, but the values in this column are all numbers. Then you may want to ensure that you only load numbers. Using data type analysis, you can have OWB derive a rule that requires all data stored within an attribute to be of the same data type.

Unique Key Analysis 

Unique key analysis provides information to assist you in determining whether or not an attribute is a unique key. It does this by looking at the percentages of distinct values that occur in the attribute. You might determine that attributes with a minimum of 70% distinct values should be flagged for unique key analysis. For example, using unique key analysis you could discover that 95% of the values in the EMP_ID column are unique. Further analysis of the other 5% reveals that most of these values are either duplicates or nulls. You could then derive a rule that requires that all entries into the EMP_ID column be unique and not null.

Functional Dependency Analysis

Functional dependency analysis reveals information about column relationships. This enables you to search for things such as one attribute determining another attribute within an object.

Table 8-3 shows the contents of the Employees table in which the attribute Dept. Location is dependent on the attribute Dept. Number. Note that the attribute Dept. Number is not dependent on the attribute Dept. Location.

Table 8-3 Employees Table

ID Name Salary Dept Number Dept Location

10

Alison

1000

10

SF

20

Rochnik

1000

11

London

30

Meijer

300

12

LA

40

John

500

13

London

50

George

200

13

London

60

Paul

600

13

London

70

Ringo

100

13

London

80

Yoko

600

13

London

90

Jones

1200

10

SF


Referential Analysis

Referential analysis attempts to detect aspects of your data objects that refer to other objects. The purpose behind this type of analysis is to provide insight into how the object you are profiling is related or connected to other objects. Because you are comparing two objects in this type of analysis, one is often referred to as the parent object and the other as the child object. Some of the common things detected include orphans, childless objects, redundant objects, and joins. Orphans are values that are found in the child object, but not found in the parent object. Childless objects are values that are found in the parent object, but not found in the child object. Redundant attributes are values that exist in both the parent and child objects.

Table 8-4 and Table 8-5 show the contents of two tables that are candidates for referential analysis. Table 8-4, "Employees Table (Child)" is the child object, which inherits from Table 8-5, "Department Table (Parent)", the parent object.

Table 8-4 Employees Table (Child)

ID Name Dept. Number City

10

Alison

17

NY

20

Rochnik

23

SF

30

Meijer

23

SF

40

Jones

15

SD


Table 8-5 Department Table (Parent)

Dept. Number Location

17

NY

18

London

20

SF

23

SF

55

HK


Referential analysis of these two objects would reveal that Dept. Number 15 from the Employees table is an orphan and Dept. Numbers 18, 20, and 55 from the Department table are childless. It would also reveal a join on the Dept. Number column.

Based on these results, you could derive referential rules that determine the cardinality between the two tables.

Custom Profiling with Data Rules

In addition to attribute analysis, functional dependency analysis, and referential analysis, OWB offers data rule profiling. Data rule profiling enables you to create rules to search for profile parameters within or between objects.

This is very powerful as it enables you to validate rules that apparently exist and are defined by the business users. By creating a data rule, and then profiling with this rule you can verify if the data actually complies with the rule, and whether or not the rule needs amending or the data needs cleansing.

For example, the HR department might define a rule that states that Income = Salary + Bonus for the Employee table shown in Table 8-6. You can then catch errors such as the one for employee Alison.

Table 8-6 Sample Employee Table

ID Name Salary Bonus Income

10

Alison

1000

50

1075 (error)

20

Rochnik

1000

75

1075

30

Meijer

300

35

335

40

Jones

1200

500

1700


See Also:

"Data Cleansing and Correction with Data Rules" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide

Six Sigma Methodology

OWB provides Six Sigma results and metrics embedded within the other data profiling results to provide a standardized approach to data quality.

See Also:

"Viewing Profile Results" under "Performing Data Profiling" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide for information on Six Sigma results

What is Six Sigma?

Six Sigma is a methodology that attempts to standardize the concept of quality in business processes. It achieves this goal by statistically analyzing the performance of business processes. The goal of Six Sigma is to improve the performance of these processes by identifying the defects, understanding them, and eliminating the variables that cause these defects.

Six Sigma metrics give a quantitative number for the number of defects for each 1,000,000 opportunities. The term "opportunities" can be interpreted as the number of records. The perfect score is 6.0. The score of 6.0 is achieved when there are only 3.4 defects for each 1,000,000 opportunities. The score is calculated using the following formula:

  • Defects Per Million Opportunities (DPMO) = (Total Defects / Total Opportunities) * 1,000,000

  • Defects (%) = (Total Defects / Total Opportunities)* 100%

  • Yield (%) = 100 - %Defects

  • Process Sigma = NORMSINV(1-((Total Defects) / (Total Opportunities))) + 1.5

    where NORMSINV is the inverse of the standard normal cumulative distribution.

Six Sigma Metrics for Data Profiling

When you perform data profiling, the number of defects and anomalies discovered are shown as Six Sigma metrics. For example, if data profiling finds that a table has a row relationship with a second table, the number of records in the first table that do not adhere to this row-relationship can be described using the Six Sigma metric.

Six Sigma metrics are calculated for the following measures in the Data Profile Editor:

  • Aggregation: For each column, the number of null values (defects) to the total number of rows in the table (opportunities).

  • Domains: For each column, the number of values that do not comply with the documented domain (defects) to the total number of rows in the table (opportunities).

  • Referential: For each relationship, the number of values that do not comply with the documented foreign key (defects) to the total number of rows in the table (opportunities).

  • Functional Dependency: For each column, the number of values that are redundant (defects) to the total number of rows in the table (opportunities).

  • Unique Key: For each unique key, the number of values that do not comply with the documented unique key (defects) to the total number of rows in the table (opportunities).

Automated Data Cleansing

OWB enables you to automatically create corrected data objects and correction mappings based on the results of data profiling. On top of these automated corrections that make use of the underlying OWB architecture for data quality, you can create your own data quality mappings to correct and cleanse source data.

See Also:

"Overview of Automatic Data Correction and Data Rules" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide

Automatic Data Correction Based on Data Profiling Results

When you perform data profiling, OWB generates corrections for the objects that you profiled. You can then decide to create corrected objects based on results of data profiling. The corrections are in the form of data rules that can be bound to the corrected object.

See Also:

"Generating Corrections Based on Data Profiling Results" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide

Types of Corrections for Source Data

You can perform the following types of corrections on source data objects:

  • Schema correction

    Schema correction creates scripts that you can use to create a corrected set of source data objects with data rules applied to them. The corrected data objects adhere to the data rules derived from the results of data profiling.

    The correction tables have names that are prefixed with TMP__. For example, when you profile the EMPLOYEES table, the correction table will be called TMP__EMPLOYEES.

  • Data Correction

    Data correction is the process of creating correction mappings to remove anomalies and inconsistencies in the source data before loading it into the corrected data objects. Correction mappings enforce the data rules defined on the data objects. While moving data from the old "dirty" tables in the profile source tables into the corrected tables, these mappings correct records that do not comply with the data rules.

    The name of the correction mapping is the object name prefixed with M_. For example, the correction mapping for the EMPLOYEE table is called M_EMPLOYEE.

Quick Summary of Performing Data Correction

To perform data correction on source data, you specify the following information:

See Also:

"Data Cleansing and Correction with Data Rules" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide for complete procedures

Data Correction Actions

Based on the data profiling results, OWB derives a set of data rules that you can use to cleanse the source data. You can automatically generate corrections based on these data rules by performing data correction actions.

For each data rule derived as a result of data profiling, you must choose a correction action that specifies how data values that are not accepted due to data rule enforcement should be handled. The correction actions you can choose are:

  • Ignore: The data rule is ignored and, therefore, no values are rejected based on this data rule.

  • Report: The data rule is run only after the data has been loaded for reporting purposes. It is similar to the Ignore option, except that a report is created that contains the values that do not adhere to the data rules. This action can be used for some rule types only.

  • Cleanse: The values rejected by this data rule are moved to an error table where cleansing strategies are applied. When you select this option, you must specify a cleansing strategy.

Cleansing Strategies for Data Correction

When you decide to automatically generate corrected objects based on data profiling results, you must specify how inconsistent data from the source should be cleansed before being stored in the corrected object. To do this, you specify a cleansing strategy for each data rule that is applied to the correction object. Error tables are used to store the records that do not conform to the data rule.

The cleansing strategy you use depends on the type of data rule and the rule configuration.

See Also:

These topics in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide:

Match and Merge Operations

OWB provides general-purpose data matching and merging capabilities that can be applied to any type of data, including data deduplication features. Matching determines which records refer to the same logical data. Warehouse Builder provides a variety of match rules to compare records. Match rules range from a simple exact match to sophisticated algorithms that can discover and correct common data entry errors. Merging consolidates matched records into a single consolidated "golden standard" record based on survivorship rules called merge rules that you select or define for creating a merged value for each column.

See Also :

"Matching, Merging, and Deduplication" in Oracle Warehouse Builder Data Modeling, ETL, and Data Quality Guide for complete procedures