# Identifiers Versus Labels

Data protocols vary over project lifetimes, and many projects involve parameter sweeps. You might see filesystem directory structures evolve naming schemes like the following1:

# let's not overthink this at first.
concentration_A_0.25/
# hierarchy is good, right?
concentration_A/0.25/
# paths are getting too long.
conc_A/0.25/
# change to percentages. clever!
conc_A/25/
conc_A/25/temp_08/
# switch order, add another parameter
temp_08/conc_A/25/conc_B/05/
# ...


Or perhaps such decisions about hierarchy are reflected in a “flat” filesystem, e.g. you see one or more of {_, -, .} as parameter delimiters in longer filenames, rather than /.

You certainly need to track where data came from and how to reproduce it. And it’s convenient to be able to visually compare two points in a state space without a lot of eye movement. Rather than compare e.g. JSON documents that each take a large on-screen area to display, you want to compare compact labels that each express a composite key in the state space.

However, this composite key can change over the lifetime of a project as new parameters/dimensions are added to the state space of measurements. You need flexible, adaptable labeling of data objects.

Labeling, however, is different than identification. What makes a good identifier? It should be easy to use (i.e., to read/share/verify), unique, permanent, fast and easy to generate, and informationally dense (i.e. compact). In addition, if security is a concern, it should be opaque/unpredictable (so people can’t guess IDs they aren’t given).2

Salient attributes here are permanent and fast and easy to generate. If you need to think about what your identifiers should look like, there’s a good chance you will find yourself re-thinking your decision. This means not only that your identifiers will not be permanent, and thus you need to deal with migrations, but they may be not fast and easy to generate because (a) not all components of your composite key may be recorded yet for a given data object, or (b) minting new identifiers is awaiting a new decision about your naming scheme.

Labels, on the other hand, can change over time. They can accumulate, each preferred by a given audience due to spoken language and/or domain expertise. One label can be marked as preferred for display by default in a given user interface.

Such labels can certainly be information-dense composite keys, facilitating rapid and text-based recognition by eye of an object record without needing to look at all the metadata associated with an object ID. Flexible labeling supports good identifiers.

This post was adapted from a note sent to my email list on Machine-Centric Science.
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1. Examples are taken from this talk about the signac data management framework, motivating its use of opaque IDs for state-space points. ↩︎

2. Geewax, J. J. (2021). Resource Identification. In API Design Patterns. O’Reilly Media. ↩︎