What is SAP ESB (Enterprise Service Bus)?

Question

Hi fellow sdners gurus…  I have been reading threads about SAP SOA and ESB. 
I do not want to start a debate on wether XI is an ESB, but more of a statement to what is SAP ESB (if XI it is, then be it).
1) What is SAP ESB (Enterprise Service Bus) today (I could not find a clear answer to is)? 
2) Who uses this SAP ESB in production currently and what kind of environment (i.e. strictly SAP backend systems, or combination of various vendors’ backend systems)?
Can someone share some light on this topic?
As a reminder, an ESB is expected to exhibit the following characteristics (source Wikipedia):
•     It is usually operating-system and programming-language agnostic; for example, it should enable interoperability between Java and .NET applications.
•     It uses XML (eXtensible Markup Language) as the standard communication language.
•     It supports web-services standards.
•     It supports various MEPs (Message Exchange Patterns) (e.g., synchronous request/response, asynchronous request/response, send-and-forget, publish/subscribe).
•     It includes adapters for supporting integration with legacy systems, possibly based on standards such as JCA
•     It includes a standardized security model to authorize, authenticate and audit use of the ESB.
•     To facilitate the transformation of data formats and values, it includes transformation services (often via XSLT or XQuery) between the format of the sending application and the receiving application.
•     It includes validation against schemas for sending and receiving messages.
•     It can uniformly apply business rules, enriching messages from other sources, the splitting and combining of multiple messages and the handling of exceptions.
•     It can provide a unified abstraction across multiple layers
•     It can route or transform messages conditionally, based on a non-centralized policy (i.e. no central rules-engine needs to be present).
•     It is monitored for various SLA (Service Level Agreement) threshold message latencies and other SLA characteristics.
•     It (often) facilitates "service classes," responding appropriately to higher and lower priority users.
•     It supports queuing, holding messages if applications are temporarily unavailable.
Your help is greatly appreciated.
Kind Regards,
Jean-Michel

Answer 1

PI or XI is the ESB from SAP side. PI is not a full pledged ESB on a reference model of ESB idea but it is the the framework SAP provide as a ESB product.
A Standard Based ESB Reference Model should fullfil the following features in a framework.
ESB Features    Service Enablement Phase (1, 2, 3)
1)     Message brokering between heterogeneous environments                     
2)     Supports asynchronous, synchronous, publish and subscribe messaging                    
3)     Supports synchronous and asynchronous bridging                    
4)     Supports message formats of SOAP                    
5)     Support for message format of SOAP with attachments                    
6)     Support for xml message                     
7)     Support for structured non-XML data                    
8)     Support for raw data message                    
9)     Support for text data message                    
10)     Sport for e-mail with attachment message                    
11)     Heterogeneous transports between service end points                    
12)     Supports for FILE protocols                    
13)     Supports for FTP protocols                     
14)     Supports for HTTP protocols                    
15)     Supports for HTTPS protocols                    
16)     Supports for Multiple JMS providers                    
17)     Supports for RMI protocols                    
18)     Supports for web service protocols                    
19)     Supports for CORBA protocols                    
20)     Supports for DCOM protocols                    
21)     Supports for E-mail (POP, SMTP, IMAP) protocols                    
22)     Support for advanced transformation engine                    
23)     Support for configuration-driven routing                    
24)     Message routing based policies                    
25)     Support for call-outs to external services to support complex routing                    
26)     Support for point-to-point routing                    
27)     Support for one-to-many routing scenarios                     
28)     Support for request response model                    
29)     Support for publish-subscribe models                    
30)     Service monitoring                    
31)     Service logging                    
32)     Service auditing with search capabilities.                    
33)     Support for capture of key statistics for message and transport attributes including message invocations, errors, and performance, volume, and SLA violations.                     
34)     Supports clusters and gathers statistics across the cluster to review SLA violations                    
35)     Support for service provisioning                     
36)     Support deployment of new versions of services dynamically through configuration                    
37)     Migrates configured services and resources between design, staging and production                    
38)     Supports multiple versions of message resources that are incrementally deployed with selective service access through flexible routing                    
39)     Configurable policy-driven security                    
40)     Supports the latest security standards for authentication, encryption-decryption, and digital signatures                    
41)     Supports SSL for HTTP and JMS transports                    
42)     Supports multiple authentication models                    
43)     Policy-driven SLA enforcement                    
44)     Establishes SLAs on a variety of attributes including                     
a.     Throughput times                    
b.     Processing volumes                    
c.     Success/failure ratios of message processes                    
d.     Number of errors                    
e.     Security violations                    
f.     Schema validation issues                     
45)     Initiates automated alerts or enables operator-initiated responses to rule violations using flexible mechanisms including                     
a.     E-mail notifications                    
b.     Triggered JMS messages                    
c.     Triggered integration processes with a JMS message                    
d.     Web services invocations with a JMS message                    
e.     Administration console alerts.                     
46)     Support for having multiple LOBs manage their own service bus based on their policies, and a service bus at an enterprise level that could act as a broker for sharing services across the various business units.                    
47)     Support for agent plug-in to support following features                    
48)     External provider’s service access for security                    
49)     External provider’s service management                     
50)     External provider’s transaction container                    
a.     External provider’s business orchestration (BPEL Engine) and business work flow service container                    
51)     Transaction support on message level                    
52)     IDE Integration                    
53)     Open standards