We use models to help us understand the world around us. Models come in many forms: architectural models, mechanical drawings, free body diagrams, software object models, maps, and even art, are some of the types of models that we use to represent the real world. We use models to represent many different types of systems, such as electrical, mechanical, environmental, cultural, and economic systems.

Real-world systems are complex. They have many interacting variables, feedback mechanisms, and linear and nonlinear behaviours. Real-world systems often have ill-defined boundaries, with external factors acting on the system that may not be well understood. In order to develop models that can help us to understand certain aspects of real-world systems, we necessarily simplify our representations of the real world in order to isolate the aspects that we’re attempting to understand. Because of these simplifications, models have limitations.

Essentially, all models are wrong, but some are useful.
George Box

Consider the following model, which is a free-body diagram that we can use to help us to understand the motion of a mechanical system:

By Hill.rick.c (Own work) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons
A simple free body diagram.

To understand the motion of this system, we can develop a system of equations (a mathematical description of the model) derived from Newton’s laws of motion. This model should describe, fairly accurately, how the system will behave at scales that humans can readily observe. However, we know that Newton’s laws of motion have limited applicability outside of the scales and speeds that humans can readily observe, so this model has a limited scope of usefulness.

Similarly, other types of models have limited scopes of usefulness. The London tube map, first designed by Harry Beck, is a well-known example of effective map design:

The London tube map.

The London tube map, though a classic example of schematic map design, has a limited scope of usefulness. It’s only useful for navigating the London Underground system in the time period for which it’s published. It’s not useful for, for example, navigating London’s surface streets, and it may have limited usefulness 20 years from now.

Prehistoric humans created art that may also have been used as maps:

Prehistoric Rock Paintings at Manda Guéli Cave, Ennedi Mountains, Chad

Paintings like these may have served as maps, as models instructing the viewer where game animals or predators might have been found. These paintings are also art, models depicting how the artists’ people interacted with their environment. Again, these models have limitations. The climate in Chad is today much different than when this painting was created, and most of the animals depicted here can no longer be found here. As a map, this model has limited usefulness because it doesn’t include a scale; it’s not easy to determine from this painting how far hunters might have to travel to find food.

Salvador Dali’s The Disintegration of the Persistence of Memory is supposed to contain representations of concepts in quantum mechanics:

A model of quantum mechanics?

As with most of Dali’s famous works, it is a very abstract model of its subject matter and, as such, has limited usefulness in describing and understanding quantum mechanics.

In economics, the formula for Gross Domestic Product (GDP) is:

GDP = C  + I  + G + (Ex – Im)

This formula is a model that describes a country’s GDP in terms of consumption (C), investment (I), government spending (G), exports (Ex), and imports (Im). While it can describe the size of a country’s GDP, this model does not describe the sectors of the country’s economy and how they interact, nor does it describe how changes in one component over time affect the other components over time. Other models must be used to provide a more complete picture of a country’s economy.

All models have limitations. Whatever type of model we’re dealing with, including and maybe especially maps, we need to be aware of the scope of usefulness and limitations of the model that we’re using.

In my  previous post , I described the various types of geodatabases that you can work with in ArcGIS Desktop. In this post, I’ll describe how to authorize geodatabases. Note: in some discussions and documentation, you’ll see both the terms “authorization” and “licensing” used interchangeably. For consistency, I’ll use the term “authorization” here. 

Personal Geodatabases

You can only use personal geodatabases 32-bit ArcGIS Desktop applications (i.e., ArcMap, ArcCatalog, ArcGlobe, and ArcScene; for brevity, I’ll just refer to ArcMap in the rest of this post). Fortunately, you can read and write personal geodatabases with any ArcGIS Desktop license level (Basic, Standard, or Advanced). The ArcGIS Desktop help has  a comprehensive guide to authorizing ArcMap . If you’re using ArcGlobe or ArcScene, you’ll also need to  authorize the 3D Analyst extension . When using personal geodatabases, you only need to authorize the client that uses the geodatabase, not the geodatabase itself.

File Geodatabases

You can use file geodatabases both in ArcMap and in ArcGIS Pro. The ArcGIS Desktop help has  a comprehensive guide to authorizing ArcGIS Pro . As with personal geodatabases, you only need to authorize the clients that use the geodatabase, not the geodatabase itself.

Desktop and Workgroup Geodatabases

Desktop and workgroup geodatabases are geodatabases that are hosted on a database server. A database server is an instance of SQL Server Express that has been configured to enable geodatabase storage.

You can only use desktop and workgroup geodatabases in ArcMap. Users with an ArcGIS Desktop Basic authorization can read data in desktop and workgroup geodatabases, and users with an ArcGIS Desktop Standard or Advanced authorization can create, read and write desktop and workgroup geodatabases.

If you want to host workgroup geodatabases on your database server, then, in addition to authorizing the clients, you must also  authorize the database server  with an ArcGIS Server Workgroup license. Without this authorization, the database server can only host desktop geodatabases.

Note that there are two main ways to obtain a workgroup database server authorization from Esri. If you have already authorized the ArcGIS Server site that will host the database server, then you can authorize the database server with the keycodes file stored on the site’s host server (see the  guide to setting up an authorizing a database server  for information on locating it). Alternatively, you can authorize the database server using an ECP number for ArcGIS Server Workgroup that you can obtain from the My Esri  website.

Enterprise Geodatabases

You can use enterprise geodatabases both in ArcMap and in ArcGIS Pro. Users with an ArcGIS Desktop Basic authorization can read data in enterprise geodatabases. Users with an ArcGIS Desktop Standard or Advanced authorization, or an ArcGIS Pro authorization, can create, read, and write enterprise geodatabases.

In order to authorize an enterprise geodatabase, you must first  authorize ArcGIS Server . Authorizing any edition of ArcGIS Enterprise (Basic, Standard, or Advanced) at the Enterprise level will enable enterprise geodatabase management.

Once ArcGIS Server is authorized, users can create and authorize enterprise geodatabases  in ArcMap  and  in ArcGIS Pro .

ArcSDE Application Server

Although you can connect to existing enterprise geodatabases via the ArcSDE application server using an ArcGIS 10.5.1 client, you can’t create new enterprise geodatabases via the ArcSDE application server.

I’ve been working on a client project recently that’s required setting up, licensing, and connecting to a number of different types of geodatabases. One of the things that I’ve discovered is that there’s not a complete and concise guide to help ArcGIS users to choose the type of geodatabase they need and then set it up. In this post, I’ve put together a concise guide to the various types of geodatabases at ArcGIS 10.5.1.

Geodatabase Types

At ArcGIS 10.5.1, you can work with the following types of geodatabases:

  • Personal geodatabase: a geodatabase stored in an Access database.
  • File geodatabase: a geodatabase stored in Esri’s file- and folder-based geodatabase storage schema.
  • Desktop geodatabase: a geodatabase stored in SQL Server Express, licensed via ArcGIS Desktop.
  • Workgroup geodatabase: a geodatabase stored in SQL Server Express, licensed via ArcGIS Enterprise Workgroup.
  • Enterprise geodatabase: a geodatabase stored in one of DB2, Informix, Oracle, PostgreSQL, or SQL Server.

At ArcGIS 10.5.1, there are two ways to connect to enterprise geodatabases: for all supported enterprise geodatabase releases (10.1 through 10.5.1), an ArcGIS client can connect to the geodatabase via “direct connect” (this is Esri’s recommended method); for enterprise geodatabase releases 10.1 through 10.2.x, an ArcGIS client can also connect to the geodatabase via the ArcSDE application server.

A Brief History of ArcSDE

ArcSDE is a server-side application that enables spatial data storage in DB2, Informix, Oracle, PostgreSQL, and SQL Server (I’ll refer to these in this article as “enterprise RDBMS”). Initially, ArcSDE was a standalone product and, in ArcGIS 8.0, the only way to work with a geodatabase in an enterprise RDBMS was through the ArcSDE application server.

At ArcGIS 8.1, Esri began adding direct connect support to ArcGIS, meaning that the client connected to the enterprise geodatabase using client-side components, not through the ArcSDE application server. Esri recommends using direct connect as the method to connect to enterprise geodatabases. 

At ArcGIS 9.2, ArcSDE ceased to be a standalone product, and was integrated into ArcGIS Desktop and ArcGIS Server (in fact, the direct connect technology used by ArcGIS Desktop is ArcSDE technology). At this point, Esri began referring to ArcSDE as a “technology”, rather than as a “product”.

The final release of the ArcSDE application server was in ArcGIS 10.2.2. Esri plans to retire ArcGIS 10.2.2 on July 1, 2019. After this date, direct connect will be the only supported way to connect to an enterprise geodatabase.

Despite the gradual deprecation of ArcSDE, there are still many instances in the ArcGIS documentation of the terms “SDE” and “ArcSDE” being used to refer to desktop, workgroup, and enterprise geodatabases. In fact, even Esri employees still sometimes use this terminology. Old habits die hard, but the lack of clarity in terminology often leads to confusion among Esri customers. In communications with our clients, I’m trying to be more disciplined in using the term “ArcSDE” only in reference to the ArcSDE application server, and the terms “desktop”, “workgroup”, and “enterprise” geodatabase as defined above.

This post generated some good discussion on GeoNet. Thanks to Joshua Bixby, Asrujit SenGupta, and Tina Morgan for their input.