Database Reference
In-Depth Information
Class
ID
Class Short
Name
Class Full Name
Class Description Text
Data Modeling Fun-
damentals
Data Model-
ing 101
An introductory class covering basic data modeling concepts and prin-
ciples.
1
Advanced Data
Modeling
Data Model-
ing 301
A fast-paced class covering techniques such as advanced normaliza-
tion and ragged hierarchies.
2
3
Tennis Basics
Tennis One
For those new to the game of tennis; learn the key aspects of the game.
4
Juggling
Learn how to keep three balls in the air at once!
Surrogate keys are frequently counters - that is, the first instance created is assigned the
unique value of
1
, the second
2
, etc. However, some surrogate keys are Globally Unique
Identifiers, or GUIDs for short. A GUID is a long and frequently randomly assigned unique
value, an example being
21EC2020-3AEA-1069-A2DD-08002B30309D
.
MongoDB ObjectId = RDBMS GUID (Surrogate Key at Physical Level)
Every MongoDB document is identified by a unique
_id
field. Although the
_id
defaults to
an ObjectId type, you may use another data type if you need to as long as it is unique within
a collection. For example, you can have Collection
A
contain a document with an _id key
of
12345
and Collection
B
contain a document with an _id key of
12345
, but Collection
A
cannot contain two documents with the _id key
12345
.
The ObjectId type is similar to a Globally Unique Identifier (GUID) in how values are often
assigned, and therefore the chance of getting a duplicate value is very rare. The ObjectId is
12 bytes long. The first four bytes capture the timestamp down to the second, the next three
bytes represent the host machine (whose value is usually hashed), and the next two bytes
