modeling

问题 Suppose I have 2 tables in a database. eg: Dog & Boss This is a many to many relationship, cause a boss can have more than 1 dog, and a dog can have more than 1 owner. I am the owner of Bobby, but so is my wife. But many to many is not allowed, so there is a helpertable: DogsPerBoss How to model this in code? Class Boss can have a collection of Dogs. Class Dog can have a collection of Bosses. --> at least, that is what I think. Perhaps there are better solutions? How about extra data that is

问题 I'm having a hard time understanding the difference between dependency and assembly(ball and socket) in UML component diagram. I googled a lot and only found this relative question : uml component diagram difference between assembly and interfaces with dependency But I don't really understand the answer to that question, I specifically want to ask : What does he mean by "definition level" and "instance level" ? I understand that there is only one diagram, are there two ? Whether there are two

问题 I have fitted a model where: Y ~ A + A^2 + B + mixed.effect(C) Y is continuous A is continuous B actually refers to a DAY and currently looks like this: Levels: 1 < 2 < 3 < 4 < 5 < 6 < 7 < 8 < 9 < 11 < 12 I can easily change the data type, but I'm not sure whether it is more appropriate to treat B as numeric, a factor, or as an ordered factor. AND when treated as numeric or ordered factor, I'm not quite sure how to interpret the output. When treated as an ordered factor, summary(my.model)

问题 Should I always have a primary key in my database tables? Let's take the SO tagging. You can see the tag in any revision, its likely to be in a tag_rev table with the postID and revision number. Would I need a PK for that? Also since it is in a rev table and not currently use the tags should be a blob of tagIDs instead of multiple entries of multiple post_id tagid pair? 回答1: You should strive to have a primary key in any non-trivial table where you're likely to want to access (or update or

问题 First off, I am pretty new to this so my method/thinking may be wrong, I have imported a xlsx data set into a data frame using R and R studio. I want to be able to loop through the column names to get all of the variables with exactly " 10 " in them in order to run a simple linear regression. So here's my code: indx <- grepl('_10_', colnames(data)) #list returns all of the true values in the data set col10 <- names(data[indx]) #this gives me the names of the columns I want Here is the for

问题 Can someone briefly explain the difference between a domain class diagram and a design class diagram? I found a explanation on Yahoo answers, but I find it quite confusing. 回答1: A domain model is called conceptual model in database modeling, while a design model is called logical model . These distinctions are also used in model-driven development, where we have a succession of three types of models: (solution-independent) domain models resulting from domain/requirements engineering in the

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问题 I currently have a large data set, for which I need to calculate a segmented regression (or fit a piecewise linear function in some similar way). However, I have both a large data set, as well as a very large number of pieces. Currently I have the following approach: Let s i be the end of segment i Let (x i ,y i ) denote the i-th data point Assume the data point x k lies within segment j, then I can create a vector from x k as (s 1 ,s 2 -s 1 ,s 3 -s 2 ,...,x k -s j-1 ,0,0,...) To do a

问题 I need to model a concrete generic class inheriting from a base generic class. First, see below: ActivityFacade should be implemented this way: public class ActivityFacade : BaseFacade<Activity, int> { } How can I model this in a VS2012 UML class diagram? Looking at the diagram, it is obvious that ActivityFacade inherits from BaseFacade, but what's not obvious is the generic type parameters that it is passing in, namely: Activity and int . 回答1: You need to add a new binding class ( BaseFacade

问题 I have such model now: receipt contains components. component contain product. The difference between component and product is, that component has quantity and measure unit: eg. component is 100g sugar - sugar is a product. So I need to make lots of components to satisfy different recipes - 100g sugar is not equal 200g sugar I wonder if I can remodel it to kick off components - in pure sql it's rather easy, but I'm trying to USE django - not making workarounds. class Receipt(models.Model):