You can access both public and private feeds using the Book Search Data API. Public feeds don't require any authentication, but they are read-only. If you want to modify user libraries, submit reviews or ratings, or add labels, then your client needs to authenticate before requesting private feeds. It can authenticate using either of two approaches: AuthSub proxy authentication or ClientLogin username/password authentication. Please refer to the Authentication section in the PHP Developer's Guide for more detail.

The Book Search Data API provides a number of feeds that list collections of books.

The most common action is to retrieve a list of books that match a search query. To do so you create a VolumeQuery object and pass it to the Books::getVolumeFeed() method.

For example, to perform a keyword query, with a filter on viewability to restrict the results to partial or full view books, use the setMinViewability() and setQuery() methods of the VolumeQuery object. The following code snippet prints the title and viewability of all volumes whose metadata or text matches the query term "domino":

$books = new Zend_Gdata_Books();
$query = $books->newVolumeQuery();

$query->setQuery('domino');
$query->setMinViewability('partial_view');

$feed = $books->getVolumeFeed($query);

foreach ($feed as $entry) {
    echo $entry->getVolumeId();
    echo $entry->getTitle();
    echo $entry->getViewability();
}

The Query class, and subclasses like VolumeQuery, are responsible for constructing feed URLs. The VolumeQuery shown above constructs a URL equivalent to the following:

http://www.google.com/books/feeds/volumes?q=keyword&min-viewability=partial

Note: Since Book Search results are public, you can issue a Book Search query without authentication.

Here are some of the most common VolumeQuery methods for setting search parameters:

setQuery(): Specifies a search query term. Book Search searches all book metadata and full text for books matching the term. Book metadata includes titles, keywords, descriptions, author names, and subjects. Note that any spaces, quotes or other punctuation in the parameter value must be URL-escaped (Use a plus (+) for a space). To search for an exact phrase, enclose the phrase in quotation marks. For example, to search for books matching the phrase "spy plane", set the q parameter to %22spy+plane%22. You can also use any of the advanced search operators supported by Book Search. For example, jane+austen+-inauthor:austen returns matches that mention (but are not authored by) Jane Austen.

setStartIndex(): Specifies the index of the first matching result that should be included in the result set. This parameter uses a one-based index, meaning the first result is 1, the second result is 2 and so forth. This parameter works in conjunction with the max-results parameter to determine which results to return. For example, to request the third set of 10 results—results 21-30—set the start-index parameter to 21 and the max-results parameter to 10. Note: This isn't a general cursoring mechanism. If you first send a query with ?start-index=1&max-results=10 and then send another query with ?start-index=11&max-results=10, the service cannot guarantee that the results are equivalent to ?start-index=1&max-results=20, because insertions and deletions could have taken place in between the two queries.

setMaxResults(): Specifies the maximum number of results that should be included in the result set. This parameter works in conjunction with the start-index parameter to determine which results to return. The default value of this parameter is 10 and the maximum value is 20.

setMinViewability(): Allows you to filter the results according to the books' viewability status. This parameter accepts one of three values: 'none' (the default, returning all matching books regardless of viewability), 'partial_view' (returning only books that the user can preview or view in their entirety), or 'full_view' (returning only books that the user can view in their entirety).

http://www.google.com/books/p/PARTNER_COBRAND_ID?q=ball

http://www.google.com/books/feeds/p/PARTNER_COBRAND_ID/volumes?q=ball+-soccer

$query =
    $books->newVolumeQuery('http://www.google.com/books/p/PARTNER_COBRAND_ID');

Google Book Search provides a number of user-specific book collections, each of which has its own feed.

The most important collection is the user's My Library, which represents the books the user would like to remember, organize, and share with others. This is the collection the user sees when accessing his or her My Library page.

$feed = $books->getUserLibraryFeed();

$query = $books->newVolumeQuery(
    'http://www.google.com/books/feeds/users' .
    '/USER_ID/collections/library/volumes');
$query->setQuery('bear');
$feed = $books->getVolumeFeed($query);

$query = $books->newVolumeQuery(
    'http://www.google.com/books/feeds/users/' .
    'USER_ID/collections/library/volumes');
$query->setCategory(
$query->setCategory('favorites');
$feed = $books->getVolumeFeed($query);

$entry = new Zend_Gdata_Books_VolumeEntry();
$entry->setId(new Zend_Gdata_App_Extension_Id(VOLUME_ID));
$books->insertVolume(
    $entry,
    Zend_Gdata_Books::MY_LIBRARY_FEED_URI
);

$books->insertVolume(
    $entry,
    Zend_Gdata_Books::MY_LIBRARY_FEED_URI
);

$books->deleteVolume($entry);