{"id":85,"date":"2026-05-26T07:38:24","date_gmt":"2026-05-26T07:38:24","guid":{"rendered":"https:\/\/www.vpascode.com\/id\/docs\/uncategorized\/plantuml-playbook\/plantuml-erd-syntax-guide\/"},"modified":"2026-07-29T08:30:40","modified_gmt":"2026-07-29T08:30:40","slug":"plantuml-erd-syntax-guide","status":"publish","type":"ld_docs","link":"https:\/\/www.vpascode.com\/id\/docs\/vpascode-docs\/plantuml-playbook\/plantuml-erd-syntax-guide\/","title":{"rendered":"PlantUML ERD Syntax Guide"},"content":{"rendered":"

What is an Entity Relationship Diagram (ERD)?<\/h2>\n

An Entity Relationship Diagram (ERD)<\/strong> is a structural blueprint used to design, document, and analyze relational databases. It visualizes the tables (entities) within a system, the specific columns (attributes) they contain, and how those tables link together. In PlantUML, ERDs are authored using the Information Engineering (IE) notation<\/strong>, which implements standard crow’s foot notation<\/strong> to represent relational constraints.<\/p>\n

Whether you are designing a microservice data store, optimizing SQL join paths, or mapping out an enterprise-wide data warehouse architecture, a text-driven UML ERD ensures your database schemas are perfectly clear. With VPasCode<\/strong>, you can define your database tables, index keys, and logical relationships using a clean, declarative syntax. The engine automatically handles table box sizing and routes your foreign key connector strings without any overlapping layout lines.<\/p>\n

Core Syntax Guide: Elements and Constructs<\/h2>\n

Building a robust IE-style ERD in PlantUML relies on structured entity blocks, explicit key designations, and crow’s foot cardinality modifiers.<\/p>\n

1. Declaring Entities (Database Tables)<\/h3>\n

You declare a database table using the entity<\/code> keyword, followed by the table name and a set of curly braces. Inside the braces, you list your table columns. To make your schema clean and readable, use a horizontal line separator (--<\/code>) to separate your primary\/foreign keys from standard data attributes:<\/p>\n

\r\n
\r\n Plantuml<\/span>\r\n \r\n <\/path><\/path><\/svg>\r\n Edit Plantuml in VPasCode<\/span>\r\n <\/a>\r\n <\/div>\r\n
\r\n 
entity \"users\" as users_table {\r\n    id : INT [PK]\r\n    --\r\n    email : VARCHAR(255)\r\n    created_at : TIMESTAMP\r\n}<\/code><\/pre>                <\/div>\r\n                
\r\n                    \r\n                        <\/path><\/path><\/svg>\r\n                        Edit Plantuml in VPasCode<\/span>\r\n                    <\/a>\r\n                <\/div>\r\n            <\/div>\r\n            \n
\"\"<\/p>\n
2. Designating Primary and Foreign Keys<\/h3>\n
While text indicators like `[PK]` or `[FK]` work well, PlantUML’s IE engine also supports visual key icons. Placing an asterisk (*<\/code>) before an attribute designates it as a **mandatory (not null)** column, while a clean text string or tag adds explicit indexing context:<\/p>\n            
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\r\n                    Plantuml<\/span>\r\n                    \r\n                        <\/path><\/path><\/svg>\r\n                        Edit Plantuml in VPasCode<\/span>\r\n                    <\/a>\r\n                <\/div>\r\n                                
\r\n                    
entity \"orders\" {\r\n    * id : INT <<PK>>\r\n    --\r\n    * user_id : INT <<FK>>\r\n    discount_code : VARCHAR(50)\r\n}<\/code><\/pre>                <\/div>\r\n                
\r\n                    \r\n                        <\/path><\/path><\/svg>\r\n                        Edit Plantuml in VPasCode<\/span>\r\n                    <\/a>\r\n                <\/div>\r\n            <\/div>\r\n            \n
\"\"<\/p>\n
3. Mapping Crow’s Foot Cardinality and Relationships<\/h3>\n
To connect tables and enforce referential integrity constraints, use a combination of dashes, brackets, and pipe characters. In IE notation, these symbols form distinct **crow’s foot** heads that represent database relationships:<\/p>\n