Where does barcode collide?

The machine-readable pattern of parallel bars and spaces printed on an item so a scanner can read a coded identifier from it. Woodland and Silver's 1952 patent Classifying apparatus and method (filed 1949) set out the first such scheme, encoding data in a pattern of lines that a light beam could decode, and the idea was later standardized for checkout as the Universal Product Code. The referent is an optical label that carries a coded identifier for an object, and it has nothing to do with a gene region that names a species, an interval diagram of topological features, or a tag sequence placed inside a neuron.[1]

Unit

One printed label encoding an identifier, read as a string of digits or characters

Recovery means

Not applicable

Measured by

Decoded optically by a scanner that reads the widths of the bars and spaces and resolves them to an identifier

A short, standardized stretch of DNA taken from an agreed gene region and used to tell one species from another. Hebert, Cywinska, Ball, and deWaard's 2003 Biological identifications through DNA barcodes proposed using a fixed segment of the mitochondrial gene cytochrome c oxidase I as a reference marker, so that an unknown specimen can be named by matching its sequence against a library of known species. The referent is a biological sequence that serves as a diagnostic marker for taxonomy, and it is not a printed label on a package, an interval diagram in mathematics, or an engineered tag inside a cell.[2]

Unit

One standardized gene segment, read as a sequence of DNA letters for a single specimen

Recovery means

Not applicable

Measured by

Amplified and sequenced from tissue, then matched against a reference library of known species sequences

A collection of intervals that records, across a range of scales, when each topological feature of a dataset appears and when it disappears. Carlsson, Zomorodian, Collins, and Guibas's 2005 Persistence barcodes for shapes introduced the term for this display, drawing each feature as a horizontal bar whose length shows how long it lasts as the scale grows, and Ghrist's 2008 Barcodes: the persistent topology of data made the tool widely known. The referent is a summary of the shape of data in the study of persistent homology, where long bars mark robust features and short bars mark noise, and it is unrelated to a scanned product label, a species marker in DNA, or a molecular tag in a neuron.[3][4]

Unit

A set of birth-to-death intervals, one bar per topological feature

Recovery means

Not applicable

Measured by

Computed from a filtration of the data by tracking the birth and death of homology features across scales

A random, unique sequence of RNA introduced into a single neuron so that the cell and its projections can be identified later by sequencing. Kebschull, Garcia da Silva, Reid, Peikon, Albeanu, and Zador's 2016 High-throughput mapping of single-neuron projections by sequencing of barcoded RNA gave each neuron a distinct sequence tag and then read those tags across brain regions to trace where each cell sends its connections. The referent is a molecular label that distinguishes one neuron from another, and it differs from a printed retail code, a standardized species marker, and a diagram of persistent features in data.[5]

Unit

One unique RNA sequence tag carried by a single neuron

Recovery means

Not applicable

Measured by

Delivered by a viral library, then recovered and counted by high-throughput sequencing across brain regions