Data Warehousing - Metadata Concepts

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What is Metadata

Metadata is simply defined as data about data. The data that are used to represent other data is known as metadata. For example the index of a book serve as metadata for the contents in the book. In other words we can say that metadata is the summarized data that leads us to the detailed data. In terms of data warehouse we can define metadata as following.

  • Metadata is a road map to data warehouse.

  • Metadata in data warehouse define the warehouse objects.

  • The metadata act as a directory.This directory helps the decision support system to locate the contents of data warehouse.

Note: In data warehouse we create metadata for the data names and definitions of a given data warehouse. Along with this metadata additional metadata are also created for timestamping any extracted data, the source of extracted data.

Categories of Metadata

The metadata can be broadly categorized into three categories:

  • Business Metadata - This metadata has the data ownership information, business definition and changing policies.

  • Technical Metadata - Technical metadata includes database system names, table and column names and sizes, data types and allowed values. Technical metadata also includes structural information such as primary and foreign key attributes and indices.

  • Operational Metadata - This metadata includes currency of data and data lineage.Currency of data means whether data is active, archived or purged. Lineage of data means history of data migrated and transformation applied on it.

Metadata Categories

Role of Metadata

Metadata has very important role in data warehouse. The role of metadata in warehouse is different from the warehouse data yet it has very important role. The various roles of metadata are explained below.

  • The metadata act as a directory.

  • This directory helps the decision support system to locate the contents of data warehouse.

  • Metadata helps in decision support system for mapping of data when data are transformed from operational environment to data warehouse environment.

  • Metadata helps in summarization between current detailed data and highly summarized data.

  • Metadata also helps in summarization between lightly detailed data and highly summarized data.

  • Metadata are also used for query tools.

  • Metadata are used in reporting tools.

  • Metadata are used in extraction and cleansing tools.

  • Metadata are used in transformation tools.

  • Metadata also plays important role in loading functions.

Diagram to understand role of Metadata.

Role of Metadata

Metadata Respiratory

The Metadata Respiratory is an integral part of data warehouse system. The Metadata Respiratory has the following metadata:

  • Definition of data warehouse - This includes the description of structure of data warehouse. The description is defined by schema, view, hierarchies, derived data definitions, and data mart locations and contents.

  • Business Metadata - This metadata has the data ownership information, business definition and changing policies.

  • Operational Metadata - This metadata includes currency of data and data lineage. Currency of data means whether data is active, archived or purged. Lineage of data means history of data migrated and transformation applied on it.

  • Data for mapping from operational environment to data warehouse - This metadata includes source databases and their contents, data extraction,data partition cleaning, transformation rules, data refresh and purging rules.

  • The algorithms for summarization - This includes dimension algorithms, data on granularity, aggregation, summarizing etc.

Challenges for Metadata Management

The importance of metadata can not be overstated. Metadata helps in driving the accuracy of reports, validates data transformation and ensures the accuracy of calculations. The metadata also enforces the consistent definition of business terms to business end users. With all these uses of Metadata it also has challenges for metadata management. The some of the challenges are discussed below.

  • The Metadata in a big organization is scattered across the organization. This metadata is spreaded in spreadsheets, databases, and applications.

  • The metadata could present in text file or multimedia file. To use this data for information management solution, this data need to be correctly defined.

  • There are no industry wide accepted standards. The data management solution vendors have narrow focus.

  • There is no easy and accepted methods of passing metadata.



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