er-diagrams | 易学教程

Open source ER diagramming tool for mysql

阅读更多关于 Open source ER diagramming tool for mysql

问题 I want to reverse engineer (import into diagram form) the database definition dump of a database I have, then since no foreign keys are defined in this particular database, I want to be able to manually create the table to table key mappings (using crow feet notation if possible). I've taken a look at MySQL Workbench, and it gets me 85% of the way there. The nice little relationship lines won't show up though, and the auto arrange is horrible. A quick search of google turns up several other

What's the relationship between the two entities?

阅读更多关于 What's the relationship between the two entities?

问题 The ER diagram for a database is given below: Now, what's the relationship between planes and flights entities? I'd say one to many, but that'd be wrong because while one plane can have more than one flights, many flights can't have one (single) plane simultaneously. So, what exactly is the relationship? I'm new to databases. Please tell me if I'm wrong. 回答1: First, your diagram isn't an ER diagram, it's a table diagram. ER diagrams must be able to represent the ER model, which supports

Which normal form does the ER Diagram guarantee?

阅读更多关于 Which normal form does the ER Diagram guarantee?

问题 Whenever a proper ER diagram is drawn for a database and then mapped to the relational schema, I was informed that it guarantees 3NF . Is this claim true? If not, can anyone provide me a counter example. Also, please tell me whether any normal form can be claimed to be strictly followed when relational schema is mapped from a perfect ER diagram? 回答1: The short answer is no. Depending on the analysis and design approach there could be examples of ER models that appear perfectly sound in ER

How to relate table with one of many others?

阅读更多关于 How to relate table with one of many others?

问题 I am little confused about my db design. I have orders table that may have records from one of many others. So is it OK to relate each tables with 1:1 to orders . Please look at orders domains and hostings table relations. My orders table rows has either a domain or hosting regarding to its orders_type value. 回答1: Are you asking if the orders should have 1:1 relationship with domains and another 1:1 relationship with hostings? If you are, the answer is no. Your hosting table has an orders_id

Single line with an arrow mark in Entity Relattionship diagram

阅读更多关于 Single line with an arrow mark in Entity Relattionship diagram

问题 What do single line with an arrow mark in ER diagram represent? 回答1: As per Bachman Notation which you are using , "For every relation a rectangle has to be drawn and every coupling is illustrated by a line that connects the relations. On the edge of each line arrows indicate the cardinality. We have 1-to-n, 1-to-1 and n-to-m" And "Cardinality use to represent the relationship between two entities." For more on cardinality Notations 回答2: E.R diagrams represent entities as boxes, and

Single line with an arrow mark in Entity Relattionship diagram

阅读更多关于 Single line with an arrow mark in Entity Relattionship diagram

What do single line with an arrow mark in ER diagram represent? As per Bachman Notation which you are using , "For every relation a rectangle has to be drawn and every coupling is illustrated by a line that connects the relations. On the edge of each line arrows indicate the cardinality. We have 1-to-n, 1-to-1 and n-to-m" And "Cardinality use to represent the relationship between two entities." For more on cardinality Notations E.R diagrams represent entities as boxes, and relationships as lines between the boxes. The ends of these lines are shaped to represent the cardinality of the

What are the basic rules for defining entities, attributes, and relationships in an ER-Diagram?

阅读更多关于 What are the basic rules for defining entities, attributes, and relationships in an ER-Diagram?

问题 My question is: In order to exist which of the following needs obligatory to have key and attribute? entity entity-type relationship-types relations (tuple with relationship-types) I know my question is a little bit odd, but I am not quite sure what are the rules by building an ER-Diagram. In other words what should mandatory be present in my diagram and what not (e.g Attributes). Thanks in advance. 回答1: In the original Entity-Relationship method, we identfy entity types and relationship

What are the basic rules for defining entities, attributes, and relationships in an ER-Diagram?

阅读更多关于 What are the basic rules for defining entities, attributes, and relationships in an ER-Diagram?

My question is: In order to exist which of the following needs obligatory to have key and attribute? entity entity-type relationship-types relations (tuple with relationship-types) I know my question is a little bit odd, but I am not quite sure what are the rules by building an ER-Diagram. In other words what should mandatory be present in my diagram and what not (e.g Attributes). Thanks in advance. In the original Entity-Relationship method, we identfy entity types and relationship/association types and their relevant attributes. When drawing an ER diagram we pick one or more groups of