Scientific Diagram Notation Reference
When you draw a pathway or mechanism diagram, the arrow you choose carries meaning: a pointed head reads as activation, a flat T-bar as inhibition, an open circle as catalysis. This page shows the correct glyph for each relationship, and tells you which symbols are backed by a formal standard you can cite versus a convention that is merely widely used.
SBGN Process Description arcs (formal standard)
The Systems Biology Graphical Notation (SBGN) Process Description language defines precise line-ending shapes for how one entity acts on a process. These are the canonical shapes; the glyphs below are drawn to match the official SBGN PD Level 1 User Manual.
| Glyph | Arc | Meaning | Line ending (per SBGN PD manual) |
|---|---|---|---|
| Consumption | A reactant is consumed by a process | A simple line with no symbol at its extremity | |
| Production | A process produces a product | A filled (solid) arrowhead | |
| Stimulation / activation | Positively affects the flux of a process | An empty (unfilled) arrowhead | |
| Catalysis | A special case of stimulation (an enzyme catalyzes a process) | An empty circle | |
| Inhibition | Negatively affects the flux of a process | A bar perpendicular to the arc (T-bar) | |
| Modulation | Affects the flux without specifying a positive or negative sign | An empty diamond | |
| Necessary stimulation | Stimulation that is required for the process to occur | A bar followed by an open arrowhead |
Notation standards & conventions
Which systems are formal, versioned standards and which are conventions. Formal standards have an official specification you can cite; conventions are widely used but not standardized.
Mechanistic, temporal biochemical processes — closest to metabolic and regulatory pathways in textbooks. Defines process nodes and nine arcs.
Maintained by: SBGN community (under COMBINE) · Level 1 (current PD version, successor to V2.0 2019 / V1.3 2015)
All relationships an entity participates in, regardless of temporal aspects. (Individual ER glyph shapes not reproduced here — see the official spec.)
Maintained by: SBGN community (under COMBINE) · Level 1 Version 2.0 (2015)
Flow of information/influence between biochemical entities — useful for perturbation effects. (Individual AF glyph shapes not reproduced here — see the official spec.)
Maintained by: SBGN community (under COMBINE) · Level 1 Version 1.2 (2015)
Pointed arrowhead = activation, flat bar/T-bar = inhibition. Formalized when a figure declares SBGN; in a bare molecular-biology figure it is a shared convention, not a standard.
Maintained by: Community practice (formalized only inside SBGN) · N/A
Participant flow through a randomized controlled trial in four stages: Enrollment → Allocation → Follow-Up → Analysis, recording counts and exclusions at each transition.
Maintained by: CONSORT Group · CONSORT 2025 (updates 2001, 2010)
International standard for electrotechnical/electronic diagram symbols. Used across Europe, China, Australia and much of Asia.
Maintained by: International Electrotechnical Commission (IEC) · Maintained symbol database (~1,900 symbols)
North American schematic symbols and reference-designation letters. Kept broadly compatible with IEC, though some device shapes differ.
Maintained by: IEEE · IEEE 315 (Inactive-Reserved since 7 Nov 2019)
Frequently asked questions
How should activation and inhibition be drawn?
In SBGN, stimulation/activation ends in an empty (unfilled) arrowhead and inhibition ends in a bar perpendicular to the line (a T-bar). Outside SBGN this same pairing is a common convention rather than a mandated standard, but following it keeps your figure readable without a legend.
Is SBGN required for pathway figures?
No — SBGN is optional. It is a formal standard you can adopt to make a pathway or mechanism figure unambiguous, with three languages (Process Description, Entity Relationship, Activity Flow). Many published figures use SBGN-like conventions without formally following the spec.
What standard governs circuit or trial-flow diagrams?
Circuit symbols are standardized by IEC 60617 (international) and IEEE/ANSI 315 (North America, now inactive-reserved). Randomized-trial participant flow follows the CONSORT flow diagram — a formal reporting standard with four stages: Enrollment, Allocation, Follow-Up, Analysis.
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