ISO/IEC TR 23951:2020

TECHNICAL ISO/IEC TR
REPORT 23951
First edition
2020-06
Information technology — Cloud
computing — Guidance for using the
cloud SLA metric model
Technologies de l'information — Informatique en nuage —
Recommandations pour l'utilisation du modèle métrique d'accord de
niveau de service (SLA) dans le Cloud
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 Structure of this document . 2
6 Motivation. 2
6.1 Preamble . 2
6.2 Audience and some user categories . 2
6.2.1 General. 2
6.2.2 Cloud service customer (CSC) . 3
6.2.3 Cloud service provider (CSP) . 3
6.2.4 Cloud service partner (CSN) . 3
6.2.5 Regulators and policy makers . 4
6.3 Usage patterns . 4
6.3.1 General. 4
6.3.2 Extract and clarify an existing metric description from an SLA . 4
6.3.3 Create and share a metric description . 4
6.3.4 Compare metric descriptions . 5
6.3.5 Share a common foundation for a set of metrics . 5
6.3.6 Build a metrics catalogue . 5
6.4 Examples of scenarios and roles involved in sharing metric definitions . 5
7 The metric model in practice: templates . 6
7.1 A brief reminder of the metric model . 6
7.2 A tabular representation . 7
7.2.1 General. 7
7.2.2 The tabular representation for the Metric element . 8
7.2.3 The tabular representation for the Expression elements . 9
7.2.4 The tabular representation for the Rule elements .10
7.2.5 The tabular representation for the Parameter elements .11
8 An example of metric definition: the cloud service mean response time metric .11
8.1 The cloud service mean response time metric: informal variant .11
8.1.1 Extracting metric elements from an SLA narrative .11
8.1.2 Using the tabular representation .12
8.1.3 Overall structure of the metric .14
8.2 The cloud service mean response time metric: more formal variant .14
8.2.1 A more formal variant of the metric .14
8.2.2 Adding a parameter .15
8.2.3 The metric rules .15
8.2.4 The metric expressions .15
8.2.5 Overall structure of the metric .17
8.2.6 Using constants .17
9 Guidelines for using the metric model with the tabular representation .19
9.1 General .19
9.2 Guideline 1 about defining expression and rule languages.20
9.3 Guideline 2 about associating rules with expressions .20
9.4 Guideline 3 about relating expressions to each other .20
9.5 Guideline 4 about the identifiers of metric elements .21
9.6 Guideline 5 about rules specifically designed to support an expression .21
9.7 Guideline 6 about the role of parameters .21
© ISO/IEC 2020 – All rights reserved iii

9.8 Guideline 7 about representing constants .22
10 The simple cloud service availability metric .22
10.1 Measuring cloud service availability .22
10.1.1 General.22
10.1.2 Overall design approach .23
10.1.3 SLA rules and metric rules .23
10.2 The simple cloud service availability metric variant Simple_SAM_1 .24
10.2.1 The Metric element .24
10.2.2 The metric rules .24
10.2.3 The metric expressions .25
10.2.4 The metric parameters .27
10.2.5 Overall structure of the metric .27
10.3 The simple cloud service availability metric variant Simple_SAM_2 .28
10.3.1 Differences in metric design and assumptions .28
10.3.2 The Metric element .29
10.3.3 The metric rules .29
10.3.4 The metric parameters .30
10.3.5 The metric expressions .31
10.3.6 Overall structure of the metric .32
10.3.7 An alternative metric design using the Configuration element option .32
Bibliography .34
iv © ISO/IEC 2020 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
li
...