Apple Newton Utilities Uživatelská příručka stáhnout pdf (Strana 445)

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CHAPTER 11

Data Storage and Retrieval

About Data Storage on Newton Devices 11-13

exclusive forms of the same endrange selector; for example, a single query spec

cannot specify both a

beginKey value and a beginExclKey value.

Another important point to understand is that there is only one

beginKey or

beginExclKey value, and only one endKey or endExclKey value associated

with any query and the cursor it returns.

Figure 11-4 Using beginExclKey and endExclKey values to specify

a subrange

Each beginKey, beginExclKey, endKey, or endExclKey speciﬁcation

evaluates to a single value that has a unique position in the sorted index key data.

This position marks one end of the range over which the cursor iterates. The cursor

never moves to a position outside the range speciﬁed by these keys.

If any endrange selectors are deﬁned for a query, the relationship of the cursor’s

entries to the endrange selectors may be summarized as follows:

entry > beginExclKey

entry ≥ beginKey

entry ≤ endKey

entry < endExclKey

You can think of these values as being used by the system in an inequality

expression to specify the range of the cursor; for example,

beginKey ≥ entry < endExclKey

Note that if a valid entry is not found at the key value speciﬁed for an endrange

selector, the cursor is positioned on the nearest entry in index key order that falls

within the range speciﬁed by the endrange selectors. For example, if a valid entry is

not found at the key value speciﬁed for a

beginKey or beginExclKey value, the

Ascending key order

Descending key order

subrange of index key values

3 4 5

beginExclKey endExclKey

1 2 ... 440 441 442 443 444 445 446 447 448 449 450 ... 941 942

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