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C H A P T E R 1
Overview
System Services
1-5
Object Storage System
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This system is key to the Newton information architecture. The object storage
system provides persistent storage for data.
Newton uses a unified data model. This means that all data stored by all applications
uses a common format. Data can easily be shared among different applications,
with no translation necessary. This allows seamless integration of applications with
each other and with system services.
Data is stored using a database-like model. Objects are stored as frames, which are
like database records. A frame contains named slots, which hold individual pieces
of data, like database fields. For example, an address card in the Names application
is stored as a frame that contains a slot for each item on the card: name, address,
city, state, zip code, phone number, and so on.
Frames are flexible and can represent a wide variety of structures. Slots in a single
frame can contain any kind of NewtonScript object, including other frames, and
slots can be added or removed from frames dynamically. For a description of
NewtonScript objects, refer to The NewtonScript Programming Language.
Groups of related frames are stored in soups, which are like databases. For example,
all the address cards used by the Names application are stored in the Names soup,
and all the notes on the Notepad are stored in the Notes soup. All the frames stored
in a soup need not contain identical slots. For example, some frames representing
address cards may contain a phone number slot and others may not.
Soups are automatically indexed, and applications can create additional indexes on
slots that will be used as keys to find data items. You retrieve items from a soup by
performing a query on the soup. Queries can be based on an index value or can
search for a string, and can include additional constraints. A query results in a
cursor--an object representing a position in the set of soup entries that satisfy the
query. The cursor can be moved back and forth, and can return the current entry.
Soups are stored in physical repositories, called stores. Stores are akin to disk
volumes on personal computers. The Newton always has at least one store--the
internal store. Additional stores reside on PCMCIA cards.
The object storage system interface seamlessly merges soups that have the same
name on internal and external stores in a union soup. This is a virtual soup that
provides an interface similar to a real soup. For example, some of the address cards
on a Newton may be stored in the internal Names soup and some may be stored in
another Names soup on a PCMCIA card. When the card is installed, those names
in the card soup are automatically merged with the existing internal names so the
user, or an application, need not do any extra work to access those additional
names. When the card is removed, the names simply disappear from the card file
union soup.
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