12 C H A P T E R   1 used to find books; for example, you can search for the books in the card cata- log by author or by classification (according to the Dewey decimal system, or some other system). But metadata does not have to be limited to one type of description. You can also find out which books are oversize and are placed on a  separate  shelf.  Knowing  which  metadata  will  become  the  most  useful  is impossible  to  say  in  advance.  To  the  librarian,  the  book  classification  is  the most important. To the historian of the printing industry, the size of the book, its age, and the number of pages will be the points of interest. It is also hard to say what is data and what is metadata. The distinction may depend on how the data is used. Now, regard the book as an object, and the information about it as an informa- tion object. A book has a number of properties, such as whether the book is available  or  not,  which  language  it  is  in,  where  it  is  in  the  library,  who  has recently borrowed it, and so on. Those properties the attributes of the book (what determines its bookness) and the values of those attributes are all part of the information object. Metadata  applications  are  similar  even  when  used  in  different  ways.  The underlying information structures are the same, irrespective of what is done with  them  when  they  are  presented  to  the  user.  This  means  that  there  are potentially an infinite number of applications, which can cover any area in the universe. Of course, it is not possible to describe all of them in one book, but it is possible to describe the general principles behind them. And so, let us look at a few scenarios. The Library Visit The  library  community  already  uses  metadata  to  a  large  extent;  indeed,  the library community has been driving the development of metadata technologies. The library card catalog is probably the best-known example of metadata in existence, and also the one with the best-established pedigree. Lisa  Simms,  for  instance,  is  studying  at  the  University  of  Hawaii  to  be  a teacher. Today, she needs to find a book by the French pedagogue C lestin Freinet, famous in Europe for his development of a participatory school sys- tem. She switches on her computer and looks up Freinet in the library search engine. It turns out that there are no books by him in the library, so she turns to the uni- versity search engine, and at the same time types in her query into her regular search engine. The regular search engine found a number of hits on phrenology, the  science of divining people s characteristics by the bumps on their heads. 69528_CH01Ix  4/6/2001 8:15 AM  Page 12