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entity that represents the attributes that are specific to any product.
We then have a relationship between Products and Product Attri-
butes that is a one-to-zero-or-more relationship (because a product
doesn't necessarily have one of these custom attributes).
Product Instance
Another problem with products is that they must be stored some-
where. Because we have bins (represented by the Bins entity) that
hold products, we need to have a relationship between Bins and
Products. The problem is that some products are so small that they
are mixed within a bin, meaning that a single bin can hold different
types of products. Other products are large enough that they re-
quire dedicated bins, but a given bin may hold several packages con-
taining that product type. And in some cases a single product takes
an entire bin (for example, a large piano-style keyboard). Finally, we
may have a product, such as a drum set, that is composed of several
pieces, and the components may be stored in multiple bins. So we
have, in effect, a many-to-many relationship. To resolve this, we cre-
ated a Product Instance entity that allows us to relate multiple prod-
ucts to multiple bins as needed.
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Product Kits
This entity addresses situations in which we have a product for sale
that is a grouping of products. For example, MVM may occasionally
run promotions to sell a guitar with an amplifier and an instrument
cable to connect them. Normally, these are individual products. We
could simply automatically generate an order that adds each item;
however, that creates problems with pricing differences (because
the point is to reduce the customer's price) between the promo-
tional price and the standard price. Additionally, if we add each item
separately, we don't have as much historical visibility into how many
of each item was sold as part of the promotion versus those sold
through a standard order. Although there are other possible solu-
tions, we chose to handle this through a separate entity that effec-
tively creates a new product composed of the promotional items.
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Product Vendors
This entity solves a similar problem as Product Instance does.
Because MVM may purchase multiple products from a specific ven-
dor, or it may buy the same product from different vendors, we have
a many-to-many relationship; this entity facilitates that relationship.
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