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This seems like a case where you'd want to use inheritance (subtype/supertype), but it isn't. A company that manufactures engines won't necessarily always be an engine manufacturer, and might not on …

A few things: An address can exist but no one lives there A person can have multiple addresses (home, job, other job, summer cottage) A company or person could be at an address Two or more people ca …

You need to decide if your categories are hierarchical (one parent) or graphical (multiple parents). For example, are "cell phones" in the category "electronics" as well as "communications"? What kin …

If a Parent Task and Subtask are essentially identical, save their rank in a hierarchy, then yes, a single table is appropriate. You can use a nullable foreign key to the primary key in the same table …

Pedantically, A table doesn't reference a foreign key, it references a table via a foreign key. It makes sense if it's necessary for the data model. Here's an example. A Sales Order is associated w …

You haven't given us much to work with here, what is the "other table" about? Let's assume it's a Custom Priority for now. To be able to set a foreign key on multiple types, you need to use Table Inh …

Read up on Table Inheritance. Here's your data model in pseudo-syntax. : means inherits. Indentation means that thing is a property of the type. AbstractParty BirthDate -- companies have "created" …

Normalization says nothing about the Decorator Pattern, as normalization is much older. Check out Table Inheritance though, which I think is more along the lines of what you're talking about. http: …

So you're going to want to store your images on a fast CDN like Cloudfront. Normally I recommend storing pictures in-database, but not 240M of them :) I'd avoid storing the whole URL, as it's likely …

Sales taxes are almost infinitely complicated, so you might want to consider using a rules engine like Drools for this. Sales Tax is a rate or an amount that is charged on the value of an item, or b …

Let's say you're a car dealer, selling cars. When a customer buys a new car, he often trades in his existing car. What data model makes more sense? A) create a sales order record for the sale, and …

Do not use a list of ids. You will regret it. Use junction tables. DDL: create table organization ( organization_id bigserial primary key, name text not null ); create table individual ( indi …

There are a few times when constraints get in the way: When you need to use Single Table Inheritance (STI). Imagine you sell to both individuals and organizations. You will need a single "Party" tab …

If you don't need to sort or search features, then using a CLOB might be fine, storing all the features as XML, which you can still query and is easy to format to HTML. If there are business rules or …

A product is not inventory. Inventory and products are distinct. A product is really a specification of a product, not a physical thing. The physical thing is an Asset that the company owns (or sto …