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58 vFoglight

Web Component Guide

can optionally be invoked to minimize the duplication required to copy the specific

view.

Observations

In general, the Web Component Framework and vFoglight are concerned with the

collection of information over time. These collections are called observations.

Observations can be of any kind of object. Observations that are handled specially by

the Web Component Framework are Metrics and Enum Observations. The scope and

quality of the information returned by an observation in the Web Component

Framework is determined by the time range used to retrieve the information.

Time Range Related to Observations

A TimeRange for the a Metric Observation can be specified in various ways, but it is

always ultimately composed of a range of date-time objects, and a granularity. The

granularity can be RAW, which means that data observations should be shown in the

metric history with the smallest available granularity, or a number of milliseconds, for

example, 300,000 for 5 minutes. It can also be AUTO, for example, a numeric value of

-2, meaning the code will pick the best granularity based on the time range.

The list of history Metric Values must be in ascending order of date-time.

When the granularity is RAW, indicated by the numeric value -1, history observations

will be added with the smallest available granularity. Different observations within the

history may cover differently-sized time intervals, and different metrics in the same

time range using RAW granularity may have different numbers of history observations

in the case of unrelated time intervals.

When the granularity is a number of milliseconds, in each history metric value, the

difference between the end time and the start time (in milliseconds) must equal the

granularity. Each successive history object’s start time should be the previous history

object’s end time. That is, each history object must cover exactly one granularity

interval.

Exactly how the start times and end times of the history objects are related to the start

time and end time of the entire non-RAW time range is not specified as a Web

Component Framework requirement. For one thing, the length of the entire time range

may not be an even multiple of the granularity. Reasonable options include starting the

first history object’s start time at the exact start time of the time range, or starting it at

the start time of the time range, less half the granularity. However, the start time of the

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