Strict Database Standards and Conventions

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Strict Database Standards and Conventions

I recently read Brian Knight's “Database

Standards and Conventions”. I found

that I agreed with his recommendations, but I feel that he doesn’t go far

enough. He writes “I receive more hate mail about this article than anything

I've ever written”, so I guess I’m setting myself up for a torrent of criticism

in publishing this…

Background

I learned this standard in 1996 when I started work on a

project for a large insurance company here in Sweden. Since then, I have since

used these conventions on just about every project I have worked on, and I have

learned to love them. Feel free to contact me with any thoughts or comments on

mattias@cambrianlabs.com. I work as a senior applications developer for

Cambrian Labs AB in Stockholm, Sweden.

Modules

First off, when your conceptual database design is more or

less done, divide it into modules. What modules you use totally depend on what

kind of database you’re designing. For instance; you could have one module for

contacts (addresses to companies and individuals), one module for products, one

module for contracts, one module for agents and so on. As a simple rule, tables

should more often reference tables within it’s module than tables outside it. If

they don’t, they probably belong in another module. Keep the modules fairly

small (perhaps 3 to 25 tables), otherwise the advantages are lost.

 

This also helps to conceptualize the database design,

learning how the system works is easier one module at a time, than the entire

system all at once. They can also be used when several people are working on the

same project - work can easily be divided along module boundaries.

 

Number the modules 01, 02, 03 and so on. These module

numbers will be used when naming tables.

Tables

Tables are also numbered, but their number is unique within

the module, not across modules. That means that table 01 can exist in many

modules - but they will still be unique in combination with the module numbers.

The name of the table should be T + module number + table number + “_” +

descriptive name. For instance

·        

T0101_CONTACT  = the first table in the first module

·        

T0102_CONTACT_TYPE = the second table in first module

·        

T0201_ARTICLE = the first table in the second module

·        

T0202_ARTICLE_AUTHOR = the second table in the second module

 

This has many advantages;

·        

the tables will be sorted in the module order in the Enterprise

Manager

·        

finding a particular table in a long list of tables is easy when

you just have to match the prefix

·        

it’s easy to tell to what module a table belongs, and therefore

what it does

 

Don’t worry, you’ll memorize the prefix of any frequently

used table very fast.

 

I find that I sometimes forget the name of tables I haven’t

used in a while, and listing all tables (when there are many) doesn’t really

help finding that one table I need. But I always remember what module the table

belongs to, so I just write sp_tables “T05%” (or actually, I write tables_like

T05, which is a script much like sp_tables, but it lists the table names first,

so I don’t have to scroll a lot ;)). Out pops something like 10 to 20 tables,

and picking out the one I need is a breeze.

 

Two tables should never have the same prefix, that would

make things much more difficult in the future. If you find that you have, by

mistake, created two tables with the same prefix, correct the mistake as soon as

possible, also correcting the column names!

Column names

When creating columns, their names are prefixed with the

table prefix. The only exception is foreign keys, but more on that later. So,

the name would be table prefix + “_”  + descriptive name. The table

T0101_CONTACT would contain columns like T0101_NAME, T0101_ADRESS_1 and so on.

When you join two tables, there’s never any question to which table a certain

column belongs. It’s not even an issue – it’s obvious from the column name.

 

If there is a simple primary key (simple as in a single

column), then it is treaded as a special case. If the key is an identity column,

it’s named table name + “_” +  id. It would be T0101_CONTACT_ID in this

case. If it’s a code of some kind, it’s named table name + “_” + code.

This is because the primary key is often referenced in foreign keys, and

therefore the full name is very useful to have, as I’ll show below.

 

As Brian Knight suggests in his paper, abbreviations should

be used sparingly, and using underscore between names is good practice. Oh, if

you forget to add an underscore somewhere in a column name and don’t go back and

change it, then it will come back and bite you. Remembering that one

exception, where there wasn’t an underscore, is very difficult.

Foreign keys

When adding a foreign key (a column that references the

primary key on another table) to a table, the column should have the name of the

original column. If my T0101_CONTACT table refers to a T0102_CONTACT_TYPE, then

the column should be named T0102_CONTACT_TYPE_ID (assuming it is the primary key

of T0102_CONTACT_TYPE).  This has huge advantages;

·        

It’s always obvious what table a foreign key refers to

·        

It’s always obvious what columns actually are foreign keys

(as they have a different prefix)

·        

When joining two tables, you have most (if not all) of the

information you’ll be needing to write the query

·        

When creating the relational integrity diagram in the enterprise

manager, you’re always connecting two keys of identical names, so no searching

is required - it’s the default selection in the editor.

 

For instance, running the query “select * from

T0101_CONTACT”, it is immediately obvious that it contains a foreign key called

“ T0102_CONTACT_TYPE_ID”. It’s “obviously” a foreign key because it has a

different prefix. It’s also obvious that it refers to a table called

T0102_CONTACT_TYPE. Therefore it would be possible to write a join between these

two tables without doing any more research;

 

select

  *

from

  T0101_CONTACT,

  T0102_CONTACT_TYPE

where

 

T0101_CONTACT.T0102_CONTACT_TYPE_ID =

   

T0102_CONTACT_TYPE.T0102_CONTACT_TYPE_ID

 

When one table contains two foreign keys to the same table

they’re named with the original column name plus a descriptive text – as always,

separated with an underscore.

Naming views

The naming convention of views is very similar to that of

tables, except the prefix is V instead of T. This makes it “V” + module

number + view number + “_” + descriptive name

 

However, it’s rather convenient to have views named like

the table they’re looking at (with the V instead of the T) and maybe a

description of what they do. This way they’re easy to remember, and they’re easy

to find. You remember the name and the number of the table, just look for views

with the same number prefixes and you’re home. This would violate the numbering

scheme in case there was more than one view per table. Also, if the view looks

at many tables (as the most often do), which of these tables should supply the

prefix?

Naming stored procedures

Again, the naming convention of stored procedures is very

similar to that of tables, but we prefix them with a P, as in “P” + module

number + stored procedure number + “_” + descriptive name.

In closing

If you were with me this far, I would like to thank you for

taking the time to read this. I hope you at least found some small piece of

wisdom among all these many words.

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