Download Manifest Video
Charles Holley
You can use a manifest to make sure that the COPY command loads all of the required files, and only the required files, for a data load. You can use a manifest to load files from different buckets or files that do not share the same prefix. Instead of supplying an object path for the COPY command, you supply the name of a JSON-formatted text file that explicitly lists the files to be loaded. The URL in the manifest must specify the bucket name and full object path for the file, not just a prefix.
A manifest created by an UNLOAD operation using the MANIFEST parameter might have keys that are not required for the COPY operation. For example, the following UNLOAD manifest includes a meta key that is required for an Amazon Redshift Spectrum external table and for loading data files in an ORC or Parquet file format. The meta key contains a content_length key with a value that is the actual size of the file in bytes. The COPY operation requires only the url key and an optional mandatory key.
This specification defines a JSON-based file format that provides developers with a centralized place to put metadata associated with a web application. This metadata includes, but is not limited to, the web application's name, links to icons, as well as the preferred URL to open when a user launches the web application. The manifest also allows developers to declare a default screen orientation for their web application, as well as providing the ability to set the display mode for the application (e.g., in fullscreen). Additionally, the manifest allows a developer to "scope" a web application to a URL. This restricts the URLs to which the manifest is applied and provides a means to "deep link" into a web application from other applications.
The [=manifest/scope=] member tells the browser which documents are part of a web application, and which are not - and hence, to which set of web pages the manifest is "[=applied=]" when the user navigates around a web site.
For example, `"scope": "/"` means that the manifest applies to every document in an origin. On the other hand, `"scope": "/racer/"` means that only documents within the path "/racer/" are [=URL/within scope=]: so "/racer/race1.html", "/racer/race2.html", etc. would all be [=URL/within scope=], but "/elsewhere/" and anything at the root "/" would be "out of scope" and the manifest wouldn't apply to documents in those paths. Only one scope path is supported. See [[[#nav-scope]]] for the technical details.
[=Applying=] a manifest means that any members that affect presentation found in the manifest will come into effect, such as display "fullscreen", or applying a particular screen orientation. As long as the application is navigated to URLs that are [=URL/within scope=], the browser will continue to apply the manifest. However, navigating the web applications "out of scope" will cause the manifest to no longer be applied, and the browser will apply its own defaults. This will cause, for example, the application to no longer be displayed in fullscreen, and instead be displayed as a regular web page in a browser tab. It's left up to implementers to decide how to deal with web pages being navigated in and out of scope. See [[[#applying]]] for the technical details.
Finally, as it's possible that a user can install a web application from any document within an origin, it's good practice to always declare a [=manifest/scope=] member in a manifest. If the [=manifest/scope=] member is missing from the manifest, then the path of the [=manifest/start_url=] member is used as a fallback. And if the [=manifest/start_url=] member is also missing, then the document URL from which the web application is installed gets used as the scope. To be sure you don't get any unexpected navigation behavior, always include a [=manifest/scope=] member preferably set to `"/"`.
The [=manifest's=] lang member is a string in the form of a language tag that specifies the primary language for the values of the manifest's localizable members (as knowing the language can also help with directionality).
The [=manifest's=] name member is a string that represents the name of the web application as it is usually displayed to the user (e.g., amongst a list of other applications, or as a label for an icon).
The [=manifest's=] short_name member is a string that represents a short version of the name of the web application. It is intended to be used where there is insufficient space to display the full name of the web application.
The [=manifest's=] icons member are images that serve as iconic representations of the web application in various contexts. For example, they can be used to represent the web application amongst a list of other applications, or to integrate the web application with an OS's task switcher and/or system preferences.
If there are multiple equally appropriate images in [=manifest/icons=], a user agent MUST use the last one declared in order at the time that the user agent collected the list of [=manifest/icons=]. If the user agent tries to use an icon but that icon is determined, upon closer examination, to be inappropriate (e.g. because its content type is unsupported), then the user agent MUST try the next-most-appropriate icon as determined by examining the [=manifest image resource=]'s members.
The [=manifest's=] orientation member is a string that serves as the default screen orientation for all top-level browsing contexts of the web application. The possible values are those of the OrientationLockType enum, which in this specification are referred to as the orientation values (i.e., "any", "natural", "landscape", "portrait", "portrait-primary", "portrait-secondary", "landscape-primary", or "landscape-secondary").
If the user agent supports the value of the [=manifest/orientation=] member as the default screen orientation, then that serves as the default screen orientation for the life of the web application (unless overridden by some other means at runtime). This means that the user agent MUST return the orientation to the default screen orientation any time the orientation is unlocked [[SCREEN-ORIENTATION]] or the top-level browsing context is navigated.
The [=manifest's=] start_url member is a string that represents the start URL , which is URL that the developer would prefer the user agent load when the user launches the web application (e.g., when the user clicks on the icon of the web application from a device's application menu or homescreen).
The [=manifest/start_url=] member is purely advisory, and a user agent MAY ignore it or provide the end-user the choice not to make use of it. A user agent MAY also allow the end-user to modify the URL when, for instance, a bookmark for the web application is being created or any time thereafter.
It's conceivable that the [=manifest/start_url=] could be crafted to indicate that the application was launched from outside the browser (e.g., `"start_url": "index.html?launcher=homescreen"`). This can be useful for analytics and possibly other customizations. However, it is also conceivable that developers could encode strings into the start_url that uniquely identify the user (e.g., a server assigned UUID). This is fingerprinting/privacy sensitive information that the user might not be aware of.
The [=identity=] is used by user agents to uniquely identify the application universally. When the user agent sees a manifest with an [=identity=] that does not correspond to an already-installed application, it SHOULD treat that manifest as a description of a distinct application, even if it is served from the same URL as that of another application. When the user agent sees a manifest where manifest["id"] is [=url/equal=] with [=URL serializer/exclude fragmentexclude fragment true=] to the [=identity=] of an already-installed application, it SHOULD be used as a signal that this manifest is a replacement for the already-installed application's manifest, and not a distinct application, even if it is served from a different URL than the one seen previously.
Since [=manifest/id=] is resolved against [=manifest/start_url=]'s [=URL/origin=], providing "../foo", "foo", "/foo", "./foo" all resolves to the same [=identifier=]. As such, best practice is to use a leading "/" to be explicit that the id is a root-relative URL path. Also, standard encoding/decoding rules apply to the id processing algorithm, as per the [[[URL]]].
If the user agent honors the value of the [=manifest/theme_color=] member as the default theme color, then that color serves as the theme color for all browsing contexts to which the manifest is applied. However, a document may override the default theme color through the inclusion of a valid [[HTML]] [^meta^] element whose [^meta/name^] attribute value is `"theme-color"`.
The [=manifest's=] related_applications member lists related applications and serves as an indication of such a relationship between web application and related applications. This relationship is unidirectional and unless a listed application claims the same relationship, the user agent MUST NOT assume a bi-directional endorsement.
The [=manifest's=] `prefer_related_applications` member is a [=boolean=] that is used as a hint for the user agent to say that related applications should be preferred over the web application. If the `prefer_related_applications` member is set to `true`, and the user agent wants to suggest to install the web application, the user agent might want to suggest installing one of the related applications instead.
The [=manifest's=] `background_color` member describes the expected background color of the web application. It repeats what is already available in the application stylesheet but can be used by the user agent to draw the background color of a web application for which the manifest is known before the files are actually available, whether they are fetched from the network or retrieved from disk.
The [=manifest/background_color=] member is only meant to improve the user experience while a web application is loading and MUST NOT be used by the user agent as the background color when the web application's stylesheet is available.
dafc88bca6