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# Design elements - ER diagram (Chen notation)

"Chen's notation for entity–relationship modeling uses rectangles to represent entity sets, and diamonds to represent relationships appropriate for first-class objects: they can have attributes and relationships of their own. If an entity set participates in a relationship set, they are connected with a line.
Attributes are drawn as ovals and are connected with a line to exactly one entity or relationship set.
Cardinality constraints are expressed as follows:
- a double line indicates a participation constraint, totality or surjectivity: all entities in the entity set must participate in at least one relationship in the relationship set;
- an arrow from entity set to relationship set indicates a key constraint, i.e. injectivity: each entity of the entity set can participate in at most one relationship in the relationship set;
- a thick line indicates both, i.e. bijectivity: each entity in the entity set is involved in exactly one relationship.
- an underlined name of an attribute indicates that it is a key: two different entities or relationships with this attribute always have different values for this attribute.
Attributes are often omitted as they can clutter up a diagram; other diagram techniques often list entity attributes within the rectangles drawn for entity sets." [Entity–relationship model. Wikipedia]
The vector stencils library ERD, Chen's notation contains 13 symbols for drawing entity-relatinship diagrams using the ConceptDraw PRO diagramming and vector drawing software.
The example "Design elements - ER diagram (Chen notation)" is included in the Entity-Relationship Diagram (ERD) solution from the Software Development area of ConceptDraw Solution Park.
Chen's ERD
Used Solutions

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## How to Create a Timeline Diagram in ConceptDraw PRO

A Timeline is a chart which displays a project plan schedule in chronological order. A Timeline is used in project management to depict project milestones and visualize project phases, and show project progress. The graphic form of a timeline makes it easy to understand critical project milestones, such as the progress of a project schedule. Timelines are particularly useful for project scheduling or project management when accompanied with a Gantt chart. It captures the main of what the project will accomplish and how it will be done. making a project timeline is one of the most important skills a project manager needs have. Making comprehensive, accurate timelines allows you getting every project off in the best way. ConceptDraw PRO allows you to draw a timeline charts using special library.