{"id":7529,"date":"2024-09-13T16:09:15","date_gmt":"2024-09-13T14:09:15","guid":{"rendered":"https:\/\/oopm.org\/?page_id=7529"},"modified":"2024-12-30T10:34:46","modified_gmt":"2024-12-30T09:34:46","slug":"17-3-subject-and-observer-aspects-new","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=7529","title":{"rendered":"18.3 Subject and Observer Aspects"},"content":{"rendered":"
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In this section, we introduce <\/mark>two related aspects, subject<\/em> and observer<\/em>, which have to be used in tandem. Objects of classes with a subject aspect may be observed by a set of objects with an observer aspect. An observer object subscribes to certain events in the subject object, events that typically change the state of the subject object. In a case of such an event, the observer will be notified. <\/p>\n\n\n\n

As a first example, we use a a fire alarm in a shopping center with a number of shops. The fire alarm may be considered a subject to be observed by a number of stakeholders that include the nearest fire station, the owner of the shopping center and the shops in the center. As a second example, we show how to add subject and observer aspects to the bank system to monitor suspicious transactions on the accounts of the bank.<\/p>\n\n\n\n