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IBM Research - Almaden
Data Links Overview - FAQS

Past Project
What is IBM DB2 UDB's Data Links?
What is the problem domain that Data Links addresses?
What sort of applications is Data Links appropriate for?
How does an application designer use Data Links?
What flavors of file reference integrity does Data Links provide?
What flavors of file reference security access does Data Links provide?
What distributed system capabilities does Data Links support?
How is Data Links Replication integrated with DB2 UDB database replication?
Does Data Links complicate file administration tasks?
How does Data Links relate to DB2 UDB's object-relational capabilities of BLOBs, User Defined Types (UDT) and User Defined Functions (UDF)?
Is there not performance degradation when accessing files managed by Data Links?
Are there any customer references, white papers and articles on Data Links?
What IBM products incorporate Data Links technology?
Is Data Links an IBM proprietary technology?
Are there any Data Links similar products in the marketplace?
Will I get locked in to IBM DB2 UDB if I use Data Links in my applications?
What operating system platforms is Data Links currently available on?
When did Data Links become available?
What future enhancements are planned for Data Links?
How much does Data Links cost?
Who can I contact for more information about Data Links?

What is IBM DB2 UDB's Data Links?

IBM DB2 UDB's Data Links technology extends the mission-critical relational DBMS capabilities of referential integrity, value-based security, transactional consistency and coordinated backup and recovery to file systems.

Data Links manages files that reside outside the database as though they are logically within the database. It guarantees referential integrity to these external files, provides enhanced access control to them, and supports automatic and coordinated backup and restore capability within transactional environments that are crucial for data management. Data Links simplifies and reduces system administration costs and complexities, by providing a single administration point for file and database data. Data Links technology thus enables a powerful symbiotic relationship between IBM DB2 UDB and file systems.
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What is the problem domain that Data Links addresses?

Estimates vary that between 70% and 95% of data resides in file systems rather than databases, and that the Internet has exacerbated this divide in favor of file systems. Current e-business trends such as e-commerce, supply chain management, and customer relationship management, require applications that can integrate content from various DBMS and file system sources, including unstructured data. Examples of such unstructured data are audio, video, and images traditionally stored in an assortment of file formats. Organizations are being challenged to support existing & emerging applications that utilize less robust file systems, while integrating the information in these file systems into the new applications of e-business.

Data Links enables organizations to use their existing & emerging file system based applications by leaving them untouched, while enabling the same files to be integrated with database systems to meet the rigorous integrity, security and transactional demands of e-business. It does this by allowing the files to reside outside the database, while extending the umbrella of mission-critical DBMS capabilities over the files as if it were logically within the database.
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What sort of applications is Data Links appropriate for?

Data Links is a candidate for any application which involves processing information from multiple heterogeneous sources that include databases and file systems, where it is required that this information be consistent between the different sources, secure, accurate, and timely. Besides the e-commerce, customer relationship management, and supply chain management e-business applications mentioned earlier, Data Links can be used effectively in automotive and health insurance applications to integrate files such as X-rays, ECG results, vehicle damage pictures; engineering & manufacturing applications involving design documents and plans; configuration and asset management application, such as, web assets (web pages, server-side programs and templates); and the management of large volumes of scientific data residing in file systems.
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How does an application designer use Data Links?

An application designer can use Data Links to maintain a reference to an existing operating system file in a column of a DB2 table. This reference is stored via a new standard SQL data type called DATALINK, using a URL (Uniform Resource Locator) syntax. Other columns of this table would generally maintain meta data about the DATALINKed files. Typically, the application programmer would insert rows in this table with meta data about the file, and its file reference (URL syntax) in the DATALINK column. The application would then typically use an SQL query against this table on the meta data columns to locate the file(s) of interest, retrieve the file reference in the DATALINK column, and then use that URL to directly access the file using the native APIs of the file system or through a browser. For the application to update or delete to a linked file, it must first unlink the file from the DB2 UDB table before the operation is allowed to proceed. Multiple DATALINK columns can be defined for a single DB2 UDB table.
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What flavors of file reference integrity does Data Links provide?

Data Links allows an application designer the option of choosing from a range of file reference integrity options depending upon the requirements of the application. One may choose to enforce referential integrity or not for a file reference. If referential integrity enforcement is chosen, one may choose to either allow the files to be updated while linked, or made read-only while linked. Special considerations apply depending upon the exact option chosen.
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What flavors of file reference security access does Data Links provide?

At a broad level, Data Links allows an application designer the option of permitting file access to either

  • All users who have database access privileges to the particular rows in the DB2 UDB table which contains the DATALINK column. In this case, any user requiring access to a file, must first access the database to obtain a Data Links access control token before attempting to access the linked file. This model is appropriate for applications that would like the database to exclusively control all access to DATALINKed files
    or
  • All users who have access privileges to the file granted to them via the operating system mechanism. The file can be accessed with or without requiring any database access. This model is appropriate for applications that would like to maintain existing file system access modes to DATALINKed files without any database intervention or interaction.
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What distributed system capabilities does Data Links support?

Data Links has been designed to support a distributed computing environment, with capabilities that include the following:

  • A DATALINK column in a DB2 UDB table can reference one or more file systems spread over one or more file system servers associated with different operating systems such as Unix and Windows NT
  • A single DataLink Manager can be associated with DATALINK columns in one or more DB2 UDB databases
  • A DATALINK column can reference files residing in Transarc's distributed file system DCE-DFS
  • Bi-directional coordinated replication of DATALINKed files is supported in an atomic, automatic and consistent way in conjunction with DB2 UDB's database replication capabilities -- see following question for more details.
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How is Data Links Replication integrated with DB2 UDB database replication?

DB2 UDB Version 7 has been enhanced to replicate the meta data associated with DATALINKed columns, and the files referenced by the DATALINKed columns to a target site in an atomic, automatic and consistent manner. When an application updates the DATALINKed column of a row, and/or the non-DATALINKed columns in the same row, then the DB2 UDB Version 7 coordinated replication mechanism ensures that the changes to the non-DATALINKed columns, and the file associated with the DATALINKed are propagated to the target site, and applied within a single unit-of-work.
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Does Data Links complicate file administration tasks?

No. On the contrary, Data Links simplifies many of the tasks associated with managing files that are logically integrated with database information. For instance, Data Links ensures that a backup of a database is coordinated with a backup of all the files referenced in that database i.e. a point-in-time image is captured for the combination of database and file data. In the same vein, a restore of the database from a backup results in Data Links automatically restoring the corresponding content of the files, thereby guaranteeing consistency. Contrast this with other systems where the onus of keeping the database and file systems synchronized is left to the database administrator and prone to error -- thus potentially jeopardizing the integrity of the information and the application.
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How does Data Links relate to DB2 UDB's object-relational capabilities of Blobs, User Defined Types (UDT) and User Defined Functions (UDF)?

Data Links treats information residing in file systems as though they were logically within the database, leaving existing applications untouched. DB2 UDB's object-relational capabilities permit an application designer to either write UDFs that process files either stored within Blobs, or are referenced by a DATALINK column or a UDT. If files are stored within BLOBS, and are also currently used in existing applications, then the potential exists for synchronization problems between the BLOB and native file information. Therefore, while both features support file processing via the database, they address different application requirements, and are complementary in nature.

DB2 UDB is unique in the industry in offering the customer these two choices to best serve the custom demands of their application.
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Is there not performance degradation when accessing the contents of files managed by Data Links?

No. Data Links does not add any overhead to the file READ and WRITE operations. As described earlier, Data Links ensures referential integrity of file references from the database by intercepting file operations such as OPEN, DELETE and RENAME that could compromise the integrity of the file reference. File READ and WRITE operations do not compromise referential integrity and are therefore obscured from Data Links line of sight . Also, given that the number of file READ and WRITE operations generally outnumber the occurrences of OPEN, DELETE or RENAME on a file, the performance degradation if any is minimal to marginal.
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Are there any customer references, white papers and articles on Data Links?

Data Links technology has been received enthusiastically in the engineering design and manufacturing community to manage their voluminous engineering drawings. Dassault Systèmes has implemented Data Links in their ENOVIA system, which is used widely by customers, such as, Boeing, Daimler Chrysler, and Peugot-Citroen. Please refer to the http://www.almaden.ibm.com/projects/datalinks.shtml web site for more detailed information on Data Links technology and usage.
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What IBM products incorporate Data Links technology?

Data Links technology is currently supported by DB2 UDB's Text Extenders and Websphere Application Server's Enterprise Java Beans' container managed persistence. Plans are underway to include Data Links technology in IBM Content Manager, Net.Commerce, and other upcoming products.
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Is Data Links an IBM proprietary technology?

No. While IBM invented Data Links technology in the early 1990s, the specification of the DATALINK data type has been accepted by both ANSI and ISO in SQL Part 9: Management of External Data (SQL/MED). ISO has progressed SQL/MED to final committee draft (FCD) in November 1999. If things go according to schedule, it should become a standard in late 2000.
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Are there any Data Links similar products in the marketplace?

To our knowledge, we are unique in the industry in offering this technology to our customers. It is our understanding however, that our competitors have projects underway to fill this void in their products.
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Will I get locked in to IBM DB2 UDB if I use Data Links in my applications?

No. As indicated earlier, the DATALINK specification is in ISO FCD status and is expected to become a standard in the near future. Application Designers who choose to implement DB2 UDB's Data Links, and then require to port this application to other RDBMS platforms may do so by emulating the Data Links API using the RDBMS' object-relational capabilities of user defined data types and user-defined functions. Of course, in such cases, the application would not obtain the benefits delivered by DB2 UDB's enforcement of referential integrity, access control, transaction consistency and coordinated backup and recovery -- in other words, these capabilities would either have to be written in the user-defined functions or sacrificed until the RDBMS stepped up with these capabilities.
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What operating system platforms is Data Links currently available on?

Data Links technology is currently implemented in IBM's DB2 UDB for AIX, DB2 UDB for NT and DB2 UDB for AS/400. Solaris support is planned for late 2000, with other platforms being added on a demand basis. File systems supported include AIX JFS, AIX DFS, Windows NTFS and Solaris' UFS.
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When did Data Links become available?

Data Links initially became available on the IBM AIX platform in DB2 UDB Version 5.2 in 1998
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What future enhancements are planned for Data Links?

  • We will continue to add new platform and file system support on a demand basis.
  • Functionally, we are looking at adding file-update-in-place, file transactional semantics, logical file object support, interfacing hierarchical storage management systems, and scaling the number of file servers that can be connected to a database server.
  • Other research involves the development of cutting-edge applications of the Data Links technology to enable efficient and robust intranet asset management.
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How much does Data Links cost?

Data Links is a separately priced feature of IBM's DB2 UDB product for the Windows NT and UNIX platforms. Details of current pricing can be obtained at http://www.ibm.com/software/data/db2/udb/
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