A service (サービス) delivers value by letting users receive the outcomes they want without taking on ownership or management themselves.
In IT, users often rely on just the functions they need, such as email or file storage, without owning any equipment. Delivering such services reliably to match customer needs, while managing operations and improving them continuously, is called IT service management (ITサービスマネジメント).
AnalogyA taxi passenger neither buys the car nor maintains it; they pay the fare and simply get the result of reaching their destination.
Exam points
ExamIT service management (ITサービスマネジメント) is the ongoing work of managing operations and improving them continuously so that IT services keep meeting customer requirements.
ExamThe value of a service (サービス) depends on the balance of its functions (what it can do), the warranty (保証) that keeps qualities such as availability (可用性, being usable whenever needed) in place, and its price. Keeping the service usable at any time falls on the warranty side.
ITIL is a framework that systematically collects best practices (ベストプラクティス, ways of working that have proven successful) for IT service management.
It began as a set of books compiled by a UK government agency, and the word Library in its name refers to that collection. It presents model approaches to delivering and supporting IT services, and each organization adopts them to fit its own situation.
AnalogyLike a book of standard chess openings, it gathers moves that many earlier players tried with success, and you pick the ones that suit the position.
Exam points
ExamITIL is an IT service management (ITサービスマネジメント) framework that systematically organizes proven ways of running and managing IT services.
ExamITIL emphasizes measuring and improving IT service quality continuously from the viewpoints of both the provider and the customer.
An SLA (service level agreement, サービスレベル合意書) is a document in which the service provider and the customer set out the scope of the service and the level of quality to be provided.
Example item
Example wording
Availability
99.9% or higher per month
Recovery from failures
Within 4 hours of occurrence
Help desk
Open weekdays 8:00–20:00
For example, it states in numbers the hours when the service can be used and how long recovery from a failure may take. Putting this in writing gives the provider and the customer the same understanding of what the service includes and what level is expected. The management activity of maintaining and raising the agreed level is called service level management (サービスレベル管理, SLM).
AnalogyIt is like booking a banquet hall and fixing the hours, the number of guests, and the menu in the written reservation.
How to rememberThe final A stands for Agreement.
Exam points
ExamAn SLA is a document recording what the provider and the customer have agreed on regarding the content and quality level of a service.
ExamThe provider concludes an SLA with the person responsible at the organization that uses the service.
Mix-upAn SLA is the document recording the agreement itself, while SLM (service level management) is the ongoing management activity of maintaining and raising the agreed level.
An SLO (service level objective, サービスレベル目標) is a concrete target value set for each service level item, which the provider aims to achieve.
Examples are "monthly availability of 99.9% or higher" and "screen response within 2 seconds", written as numbers that show clearly whether they were met. The level agreed in an SLA is expressed by building up these item-by-item target values.
AnalogyIt is the target time you set before running a marathon.
How to rememberThe final O stands for Objective, the target you aim at.
Exam points
ExamBecause an SLO is expressed as a quantitative value, whether it was achieved can be judged objectively afterward.
Mix-upAn SLA is the document covering the whole agreement, and an SLO is a target value set for each item within it.
SLA vs. SLO
Aspect
SLA
SLO
Key differenceWhat it is
Document covering the whole agreement
Target value for each item
Example
Agreement setting service hours, recovery time, and similar terms
An SLI (service level indicator, サービスレベル指標) is an indicator obtained by actually measuring the state of a service, and it is the basis for judging whether an SLO is being met.
SLA document
SLO monthly availability ≥ 99.9%
SLI measured availability this month
SLO response within 2 s
SLI measured response time
For each target, the actual value is measured and compared to see whether it is reached.
3 / 3
For example, the share of time a service was actually usable in a given month, or the average measured response time, is an SLI. When comparing SLIs against SLOs reveals an item that falls short, the cause is investigated and improvements follow.
AnalogyIt is the actual time shown on the clock when you cross the marathon finish line.
How to rememberThe final I stands for Indicator, which points to the current value like the needle on a gauge.
Exam points
Mix-upAn SLO is the value aimed for and decided in advance, while an SLI is the value actually measured while the service is delivered; whether the SLI reaches the SLO decides achievement.
SLO vs. SLI
Aspect
SLO
SLI
Key differenceWhat it is
Value aimed for
Value actually measured
When it is set
Decided in advance when the agreement is made
Obtained by measuring continuously during delivery
Example
Response within 2 seconds
Average measured response time of 1.4 seconds
Key points
A service delivers value so that users receive outcomes without owning or managing anything, and IT service management is the work of running services to fit customer needs and improving them continuously.
ITIL is a framework systematically gathering best practices for IT service management, a model that each organization adopts to fit its own situation.
An SLA is an agreement in which the provider and the customer set the scope and level of a service, and writing it in numbers makes it possible to check whether it is met.
Service quality is maintained by repeating the cycle of agreeing on a level, setting targets, measuring, and improving.