InStrum and Morris argue <ref>Rick Sturm, Wayne Morris "Foundations of Service Level Management", April 2000, Pearson.</ref> the authors argue that SLOs must be:
* Attainable
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* Mutually acceptable
InWhile <ref>AlexanderAndrieux Keller,et. Heikoal. Ludwigdefine "Thethe WSLASLO Framework:as Specifying"the andquality Monitoringof Serviceservice Levelaspect Agreementsof forthe Webagreement. Services"Syntactically, Journalit is an assertion over the terms of Networkthe andagreement Systemsas Management,well Volas 11,such n.qualities 1,as Marchdate and time" 2003.</ref name=":0" />. theKeller authorsand Ludwig more concisely define aan SLO as "commitment to maintain a particular state of the service in a given period" with respect to the state of the SLA parameters <ref>Alexander Keller, Heiko Ludwig "The WSLA Framework: Specifying and Monitoring Service Level Agreements for Web Services", Journal of Network and Systems Management, Vol 11, n. 1, TheyMarch also2003.</ref>. Keller and Ludwig go on to state that while service providers will most often be the lead entity in taking on SLOs there is no firm definition as such and any entity can be responsible for an SLO. Along with this an SLO can be broken down into a number of different components.
* Obliged - The entity that is required to deliver the SLO.
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* Expression - This is the actual language that defines what the SLO will be.
Optionally an EvaluationEvent maybe assigned to the SLO, an EvaluationEvent dictatesis defined as the measure by withwhich the SLO will be checked to see if it's meeting the Expression.
In <ref name=":0" /> the authors define the SLO as "the quality of service aspect of the agreement. Syntactically, it is an assertion over the terms of the agreement as well as such qualities as date and time".
SLOs should generally be specified in terms of an achievement value or service level, a target measurement, a measurement period, and where and how they are measured. As an example, "90% of calls to the helpdesk should be answered in less than 20 seconds measured over a one-month period as reported by the [[Automatic call distributor|ACD system]]". Results can be reported as a percent of time that the target answer time was achieved and then compared to the desired service level (90%).
