Apple Newton Utilities Guide de l'utilisateur télécharger pdf (Page 450)

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CHAPTER 11

Data Storage and Retrieval

11-18 About Data Storage on Newton Devices

All frames are compressed automatically when they are stored as soup entries and

all soup entries are decompressed when they are referenced. The automatic

compression and decompression of soup data reduces the amount of storage space

and run-time memory required by Newton applications.

If you add a frame that references another entry, the referenced entry is copied as a

frame into the new soup entry that is created. Similarly, if you move that entry to

another store, any data it references is moved to the new store as well.

The only way to retrieve an entry is to send the

Query message to the soup or

union soup in which the entry resides. This method returns a cursor, which is an

object that returns entries in response to messages it receives.

As ﬁrst returned by the cursor, the entry is a frame that holds references to the

entry’s data. Soup data referenced by this frame is not decompressed until it is

referenced—for example, to get or set the value of one of the entry’s slots. When a

slot in the entry is referenced, the system constructs the entire entry frame in the

NewtonScript heap.

Decompressed entries are cached in RAM until they are written back to the soup.

Applications can modify these cached entry frames directly. The system supplies

functions for modifying entries, writing them back to the soup, and manipulating

them in other ways.

For information about using entries, see the section “Using Entries” beginning on

page 11-57.

Alternatives to Soup-Based Storage 11

Although soup-based data storage offers many advantages, you may improve

your application’s performance or reduce its RAM requirements by storing data

in other formats.

There are a wide variety of trade-offs to consider when choosing a structure to

represent your application data. You are strongly advised to conduct realistic tests

with the actual data set your application uses before committing to the use of a

particular data structure. It’s also recommended that you design your application in

a way that allows you to experiment with the use of various data structures at any

point in its development.

When choosing schemes for storing your application’s data, you need to consider

factors such as:

■ the kind of data to be saved

■ the quantity of data to be saved

■ how the application accesses the data

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Apple Newton Utilities Guide de l'utilisateur Page 450

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