Should a database table always have primary keys?
A table should have a primary key so that you could identify each row uniquely with it. Technically, you can have tables without a primary key, but you’ll be breaking good database design rules.
modeling
What is the difference between a domain class diagram and a design class diagram?
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 system analysis, or inception, phase of a development project; (platform-independent) … Read more
What is the difference between attribute and property? [closed]
In general terms (and in normal English usage) the terms mean the same thing. In the specific context of HTML / Javascript the terms get confused because the HTML representation of a DOM element has attributes (that being the term used in XML for the key/value pairs contained within a tag) but when represented as … Read more
UML diagram for dependency between systems
your question is not very specific as all UML diagrams display some kind of dependency or pathway how to get data or make a call, so I’m not sure if I got substance of your question right 1. there is no such thing as one best UML diagram to show it all There is usually … Read more
Interpretation of ordered and non-ordered factors, vs. numerical predictors in model summary
This is not really a mixed-model specific question, but rather a general question about model parameterization in R. Let’s try a simple example. set.seed(101) d <- data.frame(x=sample(1:4,size=30,replace=TRUE)) d$y <- rnorm(30,1+2*d$x,sd=0.01) x as numeric This just does a linear regression: the x parameter denotes the change in y per unit of change in x; the intercept … Read more
XML Attributes vs Elements [duplicate]
There is an article titled “Principles of XML design: When to use elements versus attributes” on IBM’s website. Though there doesn’t appear to be many hard and fast rules, there are some good guidelines mentioned in the posting. For instance, one of the recommendations is to use elements when your data must not be normalized … Read more
What’s the best UML diagramming tool? [closed]
Some context: Recently for graduate school I researched UML tools for usability and UML comprehension in general for an independent project. I also model/architect for a living. The previous posts have too many answers and not enough questions. A common misunderstanding is that UML is about creating diagrams. Sure, diagrams are important, but really you … Read more
R Loop for Variable Names to run linear regression model
Ok, I’ll post an answer. I will use the dataset mtcarsas an example. I believe it will work with your dataset. First, I create a store, lm.test, an object of class list. In your code you are assigning the output of lm(.) every time through the loop and in the end you would only have … Read more