Why ArcSDE?

This posting lists some interesting points why using ArcSDE:

First, one of the primary functions of ArcSDE is that it provides the connectivity to the DBMS; meaning that the out-of-the-box ArcGIS Desktop clients, ArcIMS and ArcEngine and ArcGIS Server development environments don't need to know which DBMS you are working with or how the data is stored in the database.

Second, ArcSDE enables ArcIMS to scale by managing access by many users to subsets of a large, continuous data set.

Third, ArcSDE combined with ArcCatalog provides the mechanism to load and maintain data in an enterprise geodatabase (which is a geodatabase stored in a relational DBMS like Oracle, SQL Server, DB2, Informix).

Fourth, ArcSDE with ArcIMS provides ArcIMS Metadata Services.

Fifth, ArcSDE provides pyramiding for improved raster/image data access.

Sixth ArcSDE provides the transaction model that is required for a multi-user editing environment (long transaction, versions, disconnected editing, geodatabase replication (at 9.2), and history archiving (at 9.2)).

Lastly, ArcSDE provides low level data integrity checks (check that polygons are closed, that lines don't intersect themselves, etc) that complement the higher level data integrity checks of the geodatabase (relationships, domains, topology, traversable networks, etc.).

When feature classes should not be put into a feature dataset?

In general, it is a bad idea using feature dataset to group feature classes for the following reasons:

1) While accessing just one feature class, the whole feature dataset is locked.

2) When one feature class in the feature dataset is used, all feature classes in the feature dataset will be cached, not just the layer being using.

3) Don't put any layer/ feature class into a feature dataset unless you need it for geodatabase functionality (e.g. geometric network, topology, etc.)

Show friendly time in ArcSDE system tables

I came across a posting about time conversion in ArcSDE system tables in ESRI Support web site:

http://support.esri.com/index.cfm?fa=knowledgebase.techarticles.articleShow&d=25700

In the ArcSDE system tables, the dates are stored as a number that represents the time when the table was registered, or the layer was created, in seconds since 1970.

SELECT registration_id, table_name, OWNER, TO_CHAR(NEW_TIME(TO_DATE('1970-01-01', 'YYYY-MM-DD'),'GMT','PDT') + registration_date / 86400.0, 'Month DD, YYYY HH:MI:SS am')
FROM sde.table_registry;

SELECT LAYER_id, table_name, OWNER, TO_CHAR(NEW_TIME(TO_DATE('1970-01-01', 'YYYY-MM-DD'),'GMT','PDT') + CDATE / 86400.0, 'Month DD, YYYY HH:MI:SS am')
FROM sde.LAYERS;