According to the Oxford English Dictionary metadata is “data whose purpose is to describe and give information about other data”. Although the idea of labelling something in order to help understand what it is without having the thing itself in front of you is not particularly new, think of categorisation systems in libraries or museum depots, the origin of the term ‘metadata’ has to do with the development of computers in the 1960’s. In order to allow computer programs to run on various instead of specific machines (separating software from hardware), a way needed to be found to communicate to different systems what the data is, how it is used, what kind of relation to other data it has, and so on.

Metadata is often generated automatically. For instance, when a user of an app contacts the developer about a technical issue, the contactform usually sends some basic metadata with the bug report, like whether the phone was connected with wifi, or the amount of battery left on the device. This can help developers to quicker find patterns indicating when a certain type of problem occurs. The person sending the message however is not always aware of exactly what kind of information is automatically transferred with their message.

Sometimes metadata can be quite revealing. Even if what is shared within an mHealth app does not leave the device of the user, if the metadata that such an app is installed can be accessed by third parties, this can amount to sharing health related personal information: it makes sense to assume that someone who uses a Parkinson disease symptom tracker has Parkinson disease.

The possibilities to give information about data are incredibly vast. That means that if we want to structure our data using metadata we have to think about the purpose. In a library catalogue the color of a book is usually not included, unless perhaps when dealing with a certain edition of special historical interest. The selection of the characteristics of the data that are highlighted by the metadata influence what we can do with the data: how it can be accessed, if it can be repurposed or read by a different system. This points toward the importance of shared standards for metadata. Recently steps have been made to set standards for data and metadata related to mHealth (IEEE/ CEN).

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