Data flow diagram
Structured-analysis data flow diagrams in the Gane–Sarson notation: external entities, numbered processes, data stores and labelled flows, at any level (context diagram through level 2+). Trust boundaries are first-class, which makes the same figure a STRIDE threat model. Balance checking catches the classic defects — a store that is only ever read, a process with input and no output (a black hole) or output and no input (a miracle).
In the same space
Most users come to Data flow diagram from Visio DFD stencils, Lucidchart data flow, OWASP Threat Dragon or Microsoft TMT. flowss runs this engine in the browser — no install, shareable via URL, exportable to PNG / SVG / PDF / source.
Syntax at a glance
entity Customer
process 1 "Accept order"
store D1 "Orders"
boundary "PCI zone" { 1, D1 }
Customer -> 1 : "card details"Paste this in the Studio code pane to see Data flow diagram render live. The full grammar is at the upstream-docs link above.
Sample templates
All 13 →Level-1 flow of a patient portal across public internet, a portal DMZ and the clinical PHI network, balancing 14 nodes against 17 flows and listing all 10 boundary crossings as the attack surface.
Level-2 decomposition of card capture, tokenisation, authorisation and settlement, with the PCI cardholder data environment drawn as a trust zone so the 9 flows that enter or leave CDE scope are enumerated.
Retrieval-augmented support assistant from knowledge-base ingest to grounded answer, isolating the third-party embedding and completion APIs so the 8 flows leaving the trusted VPC — prompt text included — are counted as attack surface.
Discrete assembly plant from ERP order release to goods movement, laid out over Purdue levels 4, 3 and 2 so the 8 enterprise-to-plant hops a segmentation review has to justify are the ones the findings strip names.
Inbound trailer to outbound van at a parcel hub, proving that the scan, route and customs stores are each both written and read, and flagging the 7 flows that reach the partner network.
Enrolment to transcript in a student information system, separating the self-service portal from the system of record and showing that every transcript release writes the disclosure log the statutory return later reads.
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