<> The end of another chapter , Big homework is on the agenda .
<> The third 7 chapter —— The homework of database design is the second part of exercises after class 7,8,10,11 topic . Some of them are actually a little different from the answers .
<>7 topic
<>
There are several departments in the school , Each department has several classes and teaching and research sections , There are several teachers in each teaching and research section , Among them, some professors and associate professors each take a number of graduate students , There are several students in each class , Each student takes several courses , Each course can be selected by several students . Please use it E-R Draw a conceptual model of the school .
<>8 topic
<>
Some products are produced in a factory , Each product consists of different parts , Some parts can be used in different products , These parts are made of different raw materials , The materials used for different parts can be the same . These parts are put in the warehouse according to their different products , Raw materials are placed in several warehouses by category . Please use it E-R Picture the products of this factory , spare parts , Material Science , Conceptual model of warehouse .
The parts and warehouse of this problem are many to one , The warehouse - Parts are 1：n, But I always feel a little uncomfortable , Maybe it's true ： Each product is made up of different parts , Some parts can be used in different products , These parts are put in the warehouse according to their different products . In other words, a part can be put on different products , The categories of these products may be different , So which product category is the final part put in the warehouse , In this way, it seems that parts and warehouse have become a many to many relationship , But it's not right to think about it .
<>10 topic
<> Try to solve the problem 7 And exercises 8 In E-R Graph to relational model
This question is about the timetable , The answer code is student number （ Which student ）, But I only know which student it is , But I don't know which course number it refers to （ That's the curriculum ）, How to determine the results , Feeling and the second 3 There is a way out for the three tables that Zhang uses ?? The answer sets the code of the table made of parts to the part number and material number .
There is another problem , Another answer is part storage , Part storage （ Part number , Warehouse number , Storage capacity ）, The warehouse and parts are 1：n The relationship between , In principle, it can be merged , merge to n end , So the parts list I wrote is parts （ Part number , Part name , Warehouse name , Storage capacity ）, So here's another one ??
<>11 topic
<> On the exercises of conceptual analysis of paradigm in standardization theory 7 The candidate code of each relational pattern in the designed relational model , What paradigms do they belong to ? What update exception will occur ?
Technology
Daily Recommendation