Apple Newton Utilities User's Guide download pdf (Page 434)

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CHAPTER 11

Data Storage and Retrieval

11-2 About Data Storage on Newton Devices

Introduction to Data Storage Objects 11

Newton devices represent data as objects. The NewtonScript programming

language provides four basic object types that applications can use to

represent data:

Because immediates, binaries, and arrays are object representations of data types

common to many programming languages, they are not discussed further here. For

complete descriptions of these objects, see

The NewtonScript Programming

Language.

The frame is of particular interest, however, as it can contain any of the other

objects and is the only NewtonScript object to which you can send messages. In

addition, the following characteristics of frames make them a particularly ﬂexible

and efﬁcient way to store data:

■ Frames are sized dynamically—they grow and shrink as necessary.

■ All frames support a common set of predeﬁned NewtonScript data types that

allows them to share most data virtually transparently.

■ Dissimilar data types can be stored in a single frame.

Like a database record, a frame stores data items. An individual data item in the

frame is held in a slot, which may be thought of as a ﬁeld in the database record.

Unlike database records, however, frames need not contain the same complement

of slots.

Any slot can hold any NewtonScript data type, including strings, numeric formats,

arrays, and binary objects. Note that NewtonScript does not require that slots

declare a datatype. Slots are untyped because every NewtonScript object stores

datatype information as part of the object itself. (NewtonScript variables need not

declare a type, either, for the same reason.)

Slots can also hold other frames, as well as references to frames, slots, and

NewtonScript objects. A frame’s ability to reference other frames from its slots

allows it to inherit attributes and behaviors from ROM-based objects known as

system prototypes or “protos.” This feature of the object system also provides

dynamic slot lookup and message-passing between frames. For detailed

descriptions of NewtonScript syntax, system-supplied data types, dynamic slot

Immediate A small, immutable object such as a character, integer or

Boolean value.

Binary Raw binary data.

Array A collection of object references accessed from a

numerical index.

Frame A collection of object references accessed by name.

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