Why Use LOBs?

As applications evolve to encompass increasingly richer semantics, they encounter the need to deal with various kinds of data -- simple structured data, complex structured data, semi-structured data, unstructured data. Traditionally, the Relational model has been very successful at dealing with simple structured data -- the kind which can be fit into simple tables. Oracle has added Object-Relational features so that applications can deal with complex structured data -- collections, references, user-defined types and so on. Our queuing technologies deal with Messages and other semi-structured data. LOBs are designed to support the last piece - unstructured data.

Unstructured Data

Unstructured Data Cannot be Decomposed Into Standard Components

Unstructured data cannot be decomposed into standard components. Data about an Employee can be 'structured' into a Name (probably a character string), an Id (likely a number), a Salary and so on. But if we are given a Photo, we find that the data really consists of a long stream of 0s and 1s.These 0s and 1s are used to switch pixels on or off so that we see the Photo on a display, but they can't be broken down into any finer structure in terms of database storage.

Unstructured Data is Large

Also interesting is that unstructured data such as text, graphic images, still video clips, full motion video, and sound waveforms tend to be large -- a typical employee record may be a few hundred bytes, but even small amounts of multimedia data can be thousands of times larger.

Unstructured Data in System Files Need Accessing from the Database

Finally, some multimedia data may reside on operating system files, and it is desirable to access them from the database.

LOB Datatype Helps Support Internet Applications

Lately, with the growth of the internet and content-rich applications, it has become imperative that the database support a datatype that fulfills the following:

• Can store unstructured data

• Is optimized for large amounts of such data

• Provides a uniform way of accessing large unstructured data within the database or outside.

Two Type of LOBs Supported

Oracle8i supports the following two types of LOBs

• Those stored in the database either in-line in the table or in a separate tablespace (such as BLOB, CLOB, and NCLOB)

• Those stored as operating system files (such as BFILEs)