A machine learning service implements programmatic interfaces for a variety of operations on several entity types, such as data sources, statistics, feature processing recipes, models, and aliases. A first request to perform an operation on an instance of a particular entity type is received, and a first job corresponding to the requested operation is inserted in a job queue. Prior to the completion of the first job, a second request to perform another operation is received, where the second operation depends on a result of the operation represented by the first job. A second job, indicating a dependency on the first job, is stored in the job queue. The second job is initiated when the first job completes.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A system, comprising: one or more computing devices configured to: receive, via a particular programmatic interface of a set of programmatic interfaces implemented at a network-accessible machine learning service of a provider network, a first request from a client to perform a particular operation associated with an instance of an entity type, wherein the entity type comprises one or more of: (a) a data source to be used for a machine learning model, (b) a set of statistics to be computed from a particular data source, (c) a set of feature processing transformation operations to be performed on a specified data set, (d) a machine learning model employing a selected algorithm, (e) an alias associated with a machine learning model, or (f) a result of a particular machine learning model; insert a job object corresponding to the first request in a job queue of the machine learning service; provide an indication to the client that the first request has been accepted for execution; determine, in accordance with a first workload distribution strategy identified for the first request, a first set of provider network resources to be used to perform the particular operation; receive, prior to a completion of the particular operation indicated in the first request, a second request from the client to perform a second operation dependent on a result of the particular operation; insert a second job object corresponding to the second request in the job queue, wherein the second job object includes an indication of a dependency of the second operation on a result of the particular operation; prior to initiating execution of the second operation, provide a second indication to the client that the second request has been accepted for execution; and in response to a determination that the particular operation has been completed successfully, schedule the second operation on a second set of provider network resources. 2. The system as recited in claim 1, wherein the particular operation comprises one or more of: (a) a creation of the instance, (b) a read operation to obtain respective values of one or more attributes of the instance, (c) a modification of an attribute of the instance, (d) a deletion of the instance, (e) a search operation, or (f) an execute operation. 3. The system as recited in claim 1, wherein the particular operation comprises assignment of an alias usable by a designated group of users of the machine learning service to execute a particular machine learning model, wherein the alias comprises a pointer to the particular machine learning model, wherein at least some users of the designated group of users are not permitted to modify the pointer. 4. The system as recited in claim 1, wherein the set of programmatic interfaces comprises a representational state transfer application programming interface. 5. The system as recited in claim 1, wherein the particular operation comprises a creation of a particular data source, wherein the one or more computing devices are further configured to: generate a particular set of statistics on one or more variables of data records of the particular data source, without receiving a request from the client for the particular set of statistics; and provide, to the client, an indication of the particular set of statistics. 6. A method, comprising: performing, by one or more computing devices: receiving, via a particular programmatic interface of a set of programmatic interfaces implemented at a machine learning service, a first request from a client to perform a particular operation associated with an instance of an entity type, wherein the entity type comprises one or more of: (a) a data source to be used for generating a machine learning model, (b) a set of feature processing transformation operations to be performed on a specified data set, (c) a machine learning model employing a selected algorithm, or (d) an alias associated with a machine learning model; inserting a job corresponding to the first request in a job queue of the machine learning service; receiving, prior to a completion of the particular operation indicated in the first request, a second request from the client to perform a second operation dependent on a result of the particular operation; inserting a second job object corresponding to the second request in the job queue, wherein the second job object includes an indication of a dependency of the second operation on a result of the particular operation; and in response to determining that the particular operation has been completed successfully, scheduling the second operation. 7. The method as recited in claim 6, wherein the particular operation comprises one or more of: (a) a creation of the instance, (b) a read operation to obtain respective values of one or more attributes of the instance, (c) a modification of an attribute of the instance, (d) a deletion of the instance, (e) a search operation, or (f) an execute operation. 8. The method as recited in claim 6, wherein the particular operation comprises assignment of an alias usable by a designated group of users of the machine learning service to execute a particular machine learning model, wherein the alias comprises a pointer to the particular machine learning model, wherein at least some users of the designated group of users are not permitted to modify the pointer. 9. The method as recited in claim 6, wherein the particular operation comprises a creation of a particular data source, further comprising performing, by the one or more computing devices: generating a particular set of statistics on one or more variables of data records of the particular data source, without receiving a request from the client for the particular set of statistics; and providing, to the client, an indication of the particular set of statistics. 10. The method as recited in claim 9, further comprising performing, by the one or more computing devices: selecting a subset of the data records of the particular data source to be used to generate the particular set of statistics. 11. The method as recited in claim 6, further comprising performing, by the one or more computing devices: identifying a workload distribution strategy for the first request, wherein said identifying comprises one or more of: (a) determining a number of passes of processing a data set of the particular operation (b) determining a parallelization level for processing a data set of the particular operation, (c) determining a convergence criterion to be used to terminate the particular operation, (d) determining a target durability level for intermediate data produced during the particular operation, or (e) determining a resource capacity limit for implementing the particular operation. 12. The method as recited in claim 11, further comprising performing, by the one or more computing devices: selecting a particular set of provider network resources to implement the first workload strategy. 13. The method as recited in claim 6, further comprising performing, by the one or more computing devices: in response to determining that performing the particular operation includes an execution of a module developed by an entity external to the provider network, identifying a particular security container from which to select at least one resource to be used for the particular operation. 14. The method as recited in claim 6, further comprising performing, by the one or more computing devices: providing, to the client, an executable version of a particular machine learning model for execution at a platform outside the provider network. 15. The method as recited in claim 6, further comprising performing, by the one or more computing devices: verifying, prior to scheduling the particular operation, that a resource quota of the client has not been exhausted. 16. A non-transitory computer-accessible storage medium storing program instructions that when executed on one or more processors: receive, via a particular programmatic interface of a set of programmatic interfaces implemented at a network-accessible machine learning service of a provider network, a first request from a client to perform a particular operation associated with an instance of an entity type, wherein the entity type comprises one or more of: (a) a data source to be used for generating a machine learning model, (b) a set of statistics to be computed from a particular data source, (c) a machine learning model employing a selected algorithm, or (d) an alias associated with a machine learning model; insert a job corresponding to the first request in a job queue of the machine learning service; receive, prior to a completion of the particular operation indicated in the first request, a second request from the client to perform a second operation dependent on a result of the particular operation; and insert a second job object corresponding to the second request in the job queue, wherein the second job object includes an indication of a dependency of the second operation on a result of the particular operation. 17. The non-transitory computer-accessible storage medium as recited in claim 16, wherein the particular operation comprises assignment of an alias usable by a designated group of users of the machine learning service to execute a particular machine learning model, wherein the alias comprises a pointer to the particular machine learning model, wherein at least some users of the designated group of users are not permitted to modify the pointer. 18. The non-transitory computer-accessible storage medium as recited in claim 16, wherein the particular operation comprises a creation of a particular data source, wherein the instructions when executed at the one or more processors: generate a particular set of statistics on one or more variables of data records of the particular data source, without receiving a request from the client for the particular set of statistics; and provide, to the client, an indication of the particular set of statistics. 19. The non-transitory computer-accessible storage medium as recited in claim 18, wherein one or more variables comprise a plurality of variables, and wherein the instructions when executed on the one or more processors: identify, based at least in part on a correlation analysis of the plurality of variables, a first set of candidate variables to be used in preference to a second set of variables as inputs to a machine learning model; and provide an indication of the first set of variables to the client. 20. The non-transitory computer-accessible storage medium as recited in claim 16, wherein the particular operation comprises an instantiated of a particular machine learning model in online mode, wherein the instructions when executed on the one or more processors: select a set of provider network resources to be used for the particular machine learning model in online mode based at least in part on an expected workload level indicated by the client. 21. The non-transitory computer-accessible storage medium as recited in claim 16, wherein the instructions when executed on the one or more processors: receive, from the client of the service, credentials to be used to decrypt one or more data records of a particular data source to perform the particular operation. 22. The non-transitory computer-accessible storage medium as recited in claim 16, wherein the instructions when executed on the one or more processors: receive a third request from the client via an idempotent programmatic interface of the set of programmatic interfaces to perform a third operation; determine, based on one or more of: (a) an instance identifier indicated in the third request, (b) an identifier of the client, or (c) a representation of input parameters of the third request, whether the third request is a duplicate of an earlier-submitted request; and in response to a determination that the third request is a duplicate of an earlier-submitted request, provide an indication of success of the third request to the client, without inserting an additional job object corresponding to the third request in the job queue.