Add attributes page

Author: kabilar

docs/src/design/attribute-types.md

@@ -1,3 +1,88 @@
-## Work in progress
-You may ask questions in the chat window below or
-refer to [legacy documentation](https://docs.datajoint.org/)
+# Datatypes
+
+DataJoint supports the following datatypes.
+To conserve database resources, use the smallest and most restrictive datatype 
+sufficient for your data.
+This also ensures that only valid data are entered into the pipeline.
+
+## Most common datatypes
+
+-  `tinyint`: an 8-bit integer number, ranging from -128 to 127.
+-  `tinyint unsigned`: an 8-bit positive integer number, ranging from 0 to 255.
+-  `smallint`: a 16-bit integer number, ranging from -32,768 to 32,767.
+-  `smallint unsigned`: a 16-bit positive integer, ranging from 0 to 65,535.
+-  `int`: a 32-bit integer number, ranging from -2,147,483,648 to 2,147,483,647.
+-  `int unsigned`: a 32-bit positive integer, ranging from 0 to 4,294,967,295.
+-  `enum`: one of several explicitly enumerated values specified as strings.
+   Use this datatype instead of text strings to avoid spelling variations and to save 
+   storage space.
+   For example, the datatype for an anesthesia attribute could be 
+   `enum("urethane", "isoflurane", "fentanyl")`.
+   Do not use enums in primary keys due to the difficulty of changing their definitions 
+   consistently in multiple tables.
+
+-  `date`: date as `'YYYY-MM-DD'`.
+-  `time`: time as `'HH:MM:SS'`.
+-  `datetime`: Date and time to the second as `'YYYY-MM-DD HH:MM:SS'`
+-  `timestamp`: Date and time to the second as `'YYYY-MM-DD HH:MM:SS'`.
+   The default value may be set to `CURRENT_TIMESTAMP`.
+   Unlike `datetime`, a `timestamp` value will be adjusted to the local time zone.
+
+-  `char(N)`: a character string up to *N* characters (but always takes the entire *N* 
+bytes to store).
+-  `varchar(N)`: a text string of arbitrary length up to *N* characters that takes 
+*M+1* or *M+2* bytes of storage, where *M* is the actual length of each stored string.
+-  `float`: a single-precision floating-point number.
+   Takes 4 bytes.
+   Single precision is sufficient for many measurements.
+
+-  `double`: a double-precision floating-point number.
+   Takes 8 bytes.
+   Because equality comparisons are error-prone, neither `float` nor `double` should be 
+   used in primary keys.
+-  `decimal(N,F)`: a fixed-point number with *N* total decimal digits and *F* 
+fractional digits.
+   This datatype is well suited to represent numbers whose magnitude is well defined 
+   and does not warrant the use of floating-point representation or requires precise 
+   decimal representations (e.g. dollars and cents).
+   Because of its well-defined precision, `decimal` values can be used in equality 
+   comparison and be included in primary keys.
+
+-  `longblob`: arbitrary numeric array (e.g. matrix, image, structure), up to 4 
+[GiB](http://en.wikipedia.org/wiki/Gibibyte) in size.
+   Numeric arrays are compatible between MATLAB and Python (NumPy).
+   The `longblob` and other `blob` datatypes can be configured to store data 
+   [externally](../../sysadmin/external-store.md) by using the `blob@store` syntax.
+
+## Less common (but supported) datatypes
+
+-  `decimal(N,F) unsigned`: same as `decimal`, but limited to nonnegative values.
+-  `mediumint` a 24-bit integer number, ranging from -8,388,608 to 8,388,607.
+-  `mediumint unsigned`: a 24-bit positive integer, ranging from 0 to 16,777,216.
+-  `mediumblob`: arbitrary numeric array, up to 16 
+[MiB](http://en.wikipedia.org/wiki/Mibibyte)
+-  `blob`: arbitrary numeric array, up to 64 
+[KiB](http://en.wikipedia.org/wiki/Kibibyte)
+-  `tinyblob`: arbitrary numeric array, up to 256 bytes (actually smaller due to header 
+info).
+
+## Special DataJoint-only datatypes
+
+These types abstract certain kinds of non-database data to facilitate use
+together with DataJoint.
+
+- `attach`: a [file attachment](attach.md) similar to email attachments facillitating 
+sending/receiving an opaque data file to/from a DataJoint pipeline.
+
+- `filepath@store`: a [filepath](filepath.md) used to link non-DataJoint managed files 
+into a DataJoint pipeline.
+
+## Datatypes not (yet) supported
+
+-  `binary`
+-  `text`
+-  `longtext`
+-  `bit`
+
+For additional information about these datatypes, see 
+http://dev.mysql.com/doc/refman/5.6/en/data-types.html