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Is the data there when we need it in a form we can use?

We make decisions based on information; whether that is new information we have gathered (via our data acquisition systems) or knowledge and information we have in our memory, it's obvious that if the information is not where we need it when we need it, we cannot make as good a decision as we might need.

 The information might be in our files, but if we cannot retrieve it, organize it, and display it in ways that inform the decision, then the information isn't available.

 If the information has been deleted, by accident, sabotage, or systems failure, then it's not available to inform the decision.

Those might seem obvious, and they are. Key to availability requirements is that they specify what information is needed; where it will need to be displayed, presented, or put in front of the decision-makers; and within what span of time the data is both available (displayed to the decision-makers) and meaningful. Yesterday's data may not be what we need to make today's decision.

Note that availability means something different for a system than it does for the information the system produces for us. Systems availability is measurable, such as via a percentage of capacity or a throughput rate. Information availability, by contrast, tells us one of three things.

 Yes, we have what we need to know to make this decision or take this action.

 No, we do not have what we need to know, so we have to decide blindly.

 We have some of what we need to know, and we cannot logically infer that what's missing won't cause our decision to be wrong and lead us to harm.