![]() A CMS (content management system) will allow the publisher to add all kinds of metadata at various stages of the publishing process. Whoever publishes the data – inserts the data into a database – can add metadata via an application. But the LOB is still opaque – some processing needs to be done to “decorate” it with metadata, even if that metadata exists in the LOB. For example, Oracle's inter Media product will extract metadata from most common document, audio, video, and image formats and make that metadata available for query in columns of a table. This metadata can be extracted programmatically and written into database columns as the data is inserted. – and some metadata that can be added by the author. Text formats (PDF, Microsoft Word) generally contain some automatically generated metadata – the author's name, document title, last modified date, etc. Some formats have metadata embedded in them. ![]() There are several ways to create the metadata: Then we can query the metadata to find a particular instance of a LOB or to find out information about an instance of a LOB. Once we have the data in a LOB, we can store it in a database table and add metadata in other columns in the table. But the data is opaque i.e., nothing is known about a LOB instance except that it may be large. A LOB is handled in a special way by the database to cope with its potentially large size – typically two or four gigabytes. ![]() A binary LOB is a LOB that contains data that is not character-based, as opposed to a character LOB, or CLOB, which contains data that is in the character set of the database. LOB storage just means that the data item is stored as a single item in one place. Despite its name, a LOB has none of the useful attributes of an object. In a database this opaque chunk is often called a BLOB, or binary large object. One approach is to store the nontraditional data as an opaque chunk of data and add metadata. ![]() Jim Melton, Stephen Buxton, in Querying XML, 2006 2.3.1 Metadata
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