Data Storage and Retrieval

About Data Storage on Newton Devices

Indexes sort key values in ascending order unless the index spec frame used to
create a particular index specifies descending order.

Begin Keys and End Keys

11

Because index keys are sorted by value, you can improve the speed of an index
query significantly by limiting the range of index key values it tests. One way to do
this is to eliminate from the search any index key values that fall outside specified
minimum or maximum values. For example, you can specify a minimum index key
value used to select the first entry to be tested, causing the query to "skip over" all
lesser-valued index keys. A minimum value used in this way is defined in the query
spec as a

beginKey

value.

Similarly, you can specify a maximum index key value to be used in selecting the
last entry to be tested, causing the query to ignore entries having index keys of
greater value. A maximum value used in this way is defined in the query spec as an

endKey

value.

You can use these optional

beginKey

and

endKey

values together to specify a

subrange of index key values, as shown in Figure 11-3. Note that if an endrange
value is not specified, it is unbounded; for example, if you don't specify an

endKey

value the query result potentially includes all entries through the end of the index.

Using

beginKey

and

endKey

values to specify an index subrange

You can also define a special kind of key that is itself excluded from the valid
subrange of index values. These keys are defined as

beginExclKey

and

endExclKey

values in the query spec. Figure 11-4 depicts the use of

beginExclKey

and

endExclKey

values to define the same index subrange

shown in Figure 11-3. Note that you cannot specify both the inclusive and

Ascending key order

Descending key order

beginKey

endKey

subrange of index key values