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Bibliographic information is information about books as opposed to the books themselves. A book's title, its cover image, and its ISBN are all bibliographic information--the text of the book is not. Bibliographic information flows into the circulation manager and metadata wrangler from a variety of sources, mainly OPDS feeds and proprietary APIs. We keep track of all this information and where it came from, and when necessary we weigh it, sort it, and boil it down into a small amount of information that can be used by other parts of the system.

DataSource

A DataSource is some external entity that puts data into the system. This data generally falls into two categories:

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• Provide many Editions
• Provide many Equivalencys
• Provide many Hyperlinks
• Provide many Resources
• Provide many Classifications
• Provide many CustomLists
• Grant access to many LicensePools
• Provide many LicensePoolDeliveryMechanisms
• Generate many CoverageRecords
• Have many associated Credentials
• Have one IntegrationClient

Identifier

An Identifier provides a way to uniquely refer to a particular book. Common types of Identifier include ISBNs and proprietary IDs such as Overdrive or Bibliotheca IDs.

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• Have many Classifications representing how the book would be shelved in a bookstore or library. (See the classification subsystem.)
• Have many Measurements of quantities like quality and popularity. (See the measurement subsystem.)
• Have many HyperLinks to associated files such as cover images or descriptions. (See the linked resources subsystem.)
• Participate in many Equivalencys.
• Serve as the primary_identifier for multiple Editions.
• Serve as the identifier for many LicensePools, through Collection.
• Be associated with one Work, through Edition

Equivalency

An Equivalency is an assertion made by a DataSource that two different Identifiers refer to the same book.

• The strength of the Equivalency is a number from -1 to 1 indicating how much we trust the assertion. When Overdrive says that an Overdrive ID is equivalent to an ISBN, we give that Equivalency a strength of 1, because Overdrive got the ISBN from the publisher and assigned the Overdrive ID itself. When OCLC says that two ISBNs represent the same book, we give it a lower strength, because OCLC is frequently wrong about this. A negative strength means that the DataSource is pretty sure two Identifiers represent differentbooks.

Edition

An Edition is a collection of information about a book from a particular data source. Like most items in the "bibliographic metadata" section, it represents an opinion. If different data sources give conflicting information about a book, that's fine -- everyone has their opinion. When this happens, we create multiple Editions and we sort it out later, when it's time to make the presentation edition.

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• Has one DataSource. This is the data source whose opinions are recorded in the Edition.
• Has one Identifier, the primary_identifier. This identifies the book the data source is talking about.
• Contains basic metadata -- title, series, language, publisher, medium -- for that book.
• May have one or more Contributors, through Contribution.
• May be the presentation edition for a specific Work. The presentation edition is a synthetic Edition created by the system. We look over a bunch of Editions which are all (supposedly) talking about the same book, and consolidate it into a new Edition containing the best or most trusted metadata.

The contributor subsystem

This system basically tracks who wrote which book. There are two classes in this subsystem: Contributor and Contribution.

Contributor

A Contributor is a human being or a corporate entity who is credited with work on some Edition. The credit itself is kept in a Contribution, which ties a Contributor to an Edition.

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• Contains basic biographical information about a person or corporation. Most notably, it has both a display_name such as "Octavia Butler", the name that would go on the front of a book, and a sort_name such as "Butler, Octavia", the name that would go in a card catalog.

Contribution

A Contribution:

• Links a Contributor to an Edition.
• Contains a role describing the work the Contributor did on the Edition. Common roles include author, editor, translator, illustrator, and narrator.

The classification subsystem

This system tracks how a book might be classified in a card catalog or shelved in a bookstore. There are two classes in this subsystem: Subject and Classification.

Subject

A Subject represents a classification that someone might give a book. Subject handles a variety of classification schemes: Dewey Decimal, LLC, LCSH, BISAC, proprietary systems like Overdrive's, and free-form tags, among others. Four pieces of information might be derived from the Subject, and will be stored with the Subject if possible:

• Genre ("Billionare Romance" is a type of romance)
• Fiction/nonfiction status ("Science Fiction" is always fiction)
• Target audience ("Young Adult Fantasy" is always YA)
• Target age ("Picture books" are generally for very young children, not 12-year-olds.)

Classification

A Classification is someone's opinion that a book should be filed under a certain Subject.

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• Links a Subject to an Identifier.
• Has an associated DataSource -- this tracks whose opinion it is.
• Has an associated weight representing how certain we are that the book should be filed under this subject. The higher the number, the more certain we are. If OCLC says that a single library has filed a certain book under "Whales", we'll record that information but give it a low weight. If OCLC says that ten thousand libraries have filed this book under "Whales", then it's probably about whales.

Genre

There are many different data sources which use many different classification schemes for the same books. Rather than expose this chaos to patrons, we have defined about 150 Genres, corresponding to the sections of a large bookstore or branch library: "Romance", "Biography", and so on.

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